Process for preparing 2-naphthanoic acids and esters thereof

2-Naphtanoic acid or ester thereof is prepared by heating a compound selected from the group consisting of ketals and enol ethers or esters of an alpha-acetyl cinnamic acid or ester thereof at a temperature effective to cyclize the compound and form said 2-naphthanoic acid or ester thereof.

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
The present invention relates to a novel process for preparing 
2-naphthanoic acids, particularly substituted acids or esters thereof, by 
cyclizing a ketal or alpha-enol ether of an alpha-acetyl cinnamic acid or 
ester thereof. 
2. DESCRIPTION OF THE BACKGROUND 
Substituted 2-naphthanoic acids and esters thereof are useful as polymer 
intermediates in the chemical industry. However, the methodology for 
making these compounds is very sparse. The major problem posed by the 
synthesis of these compounds is that, for the 2-napthanoic acid 
derivatives to be useful as polymer intermediates, a second functional 
group besides the carboxyl group must be present. Moreover, such a 
functional group must be present as a specific location on the molecule. 
Thus, a single, specific isomer of a substituted 2-napthanoic acid or 
ester thereof must be produced out of a large number of distinguishable 
isomeric naphthanoic acids. The development of such a process is, 
therefore, of great significant to the industry. 
Specific 2-naphthanoic acids have been synthesized by the prior art. For 
example, see U.S. Pat. Nos. 4,594,445; 4,506,092; and 4,486,605. However, 
none of these methods are applicable to the general class of 2-naphthanoic 
acids or esters synthesized by the process of this invention. 
Accordingly, there is still a need for a simple and general process for the 
synthesis of 2-naphthanoic acids and esters thereof having a predictable 
substitution pattern. 
SUMMARY OF THE INVENTION 
The invention relates to a process for preparing a 2-naphthanoic acid or 
ester thereof of the formula 
##STR1## 
wherein R.sup.3 is H, halo or (C.sub.1 -C.sub.12)alkoxy, acyloxy, carboxy, 
carbalkoxy, acyl, alkyl or thioalkyl, and R.sup.1 is H, (C.sub.1 
-C.sub.12)alkyl, (C.sub.6 -C.sub.20)aryl, (C.sub.7 -C.sub.21)alkylaryl or 
araalkyl, said process comprising heating a compound selected from the 
group consisting of a ketal of the formula 
##STR2## 
wherein R.sup.1 and R.sup.3 are as described above, and each R.sup.2 is 
(C.sub.1 -C.sub.12)alkyl or the two R.sup.2 taken together are (C.sub.2 
-C.sub.12)alkylene, and an alpha-enol ether of ester of the formula 
##STR3## 
wherein R.sup.1 and R.sup.3 are as defined above and R.sup.2 is (C.sub.1 
-C.sub.12)alkyl at a temperature effective to cyclize the compound and 
obtain said 2-naphthanoic acid or ester thereof. 
This invention also relates to a process for preparing a 2-naphthanoic acid 
or an ester thereof which comprises reacting an alpha-acetyl cinnamic acid 
or ester thereof of the general formula 
##STR4## 
wherein R.sup.1 and R.sup.3 are as defined above, with a ketalizing agent 
selected from the group consisting of alkyl glycols and dialkyl acetals, 
dialkyl ketals, and tri-alkyl orthoesters; said cinnamic acid or ester 
thereof and said ketalizing agent being present in a proportion and under 
conditions effective to form a compound selected from the group consisting 
of a ketal of the formula defined above; and an enol-ether of the formula 
defined above; heating the thus obtained compound at a temperature 
effective to cyclize the compound and form said 2-naphthanoic acid or 
ester thereof. 
In addition, this invention also relates to a process for preparing a 
2-naphthanoic acid or ester thereof by reacting an acetoacetate ester with 
a benzaldehyde substituted with H, halo or (C.sub.1 -C.sub.12)alkyl, 
carboxy, carbalkoxy, acyloxy, acyl, alkoxy or alkylthio; said acetoacetate 
ester and said benzaldehyde being present in a proportion and under 
conditions effective to produce an alpha-acetyl cinnamic acid or ester 
thereof of the formula defined above; reacting the alpha-acetyl cinnamic 
acid or ester thereof with a ketalizing agent selected from the group 
consisting of alkyl glycols and dialkyl acetals, dialkyl ketals, and 
tri-alkyl orthoesters said cinnamic acid or ester thereof and said 
ketalizing agent being present in a proportion and under conditions 
effective to produce a compound selected from the group consisting of a 
ketal and an enol-ether of the cinnamic acid or ester thereof of the 
formulas defined above; and heating the thus obtained compound at a 
temperature effective to cyclize said compound and form said 2-naphthanoic 
acid or ester thereof. 
A more complete appreciation of the invention and many of the attendant 
advantages thereof will be readily perceived as the same becomes better 
understood by reference to the following detailed description of the 
preferred embodiments thereof. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The process of the invention for preparing a 2-naphthanoic acid or an ester 
thereof from a compound such as a ketal or an enol-ether or ester relies 
on a thermal ring closure of such compound. The cyclization may be 
performed either in the liquid or vapor phases, with the latter being 
generally perferred since it can be conducted even in the absence of a 
solvent and produces generally higher yields of product. 
When the cyclization is conducted in the vapor phase, it is done so at a 
temperature of about 150.degree. to 800.degree. C., and more preferably 
about 350.degree. to 600.degree. C., and a pressure of about 0.001 mmHg to 
3 atm, and preferably about 0.1 mmHg to atmospheric pressure. However, 
much higher temperatures can also be used without difficulty such as 
temperatures in excess of about 800.degree. C. These temperatures are 
easily attainable in an industrial environment. 
More commonly, the vapor phase cyclization reaction is conducted at ambient 
temperature using an inert gas purge to promote the transport of materials 
across a pyrolysis chamber. However, any feasible pressure below 
atmospheric pressure may suitably be employed and actually serves to 
promote the vaporization of the starting acids or esters. By means of 
example, a pressure of about 10 mmHg can be attained in an industrial 
environment. Higher pressures than those described above may also be 
employed, particularly in the case where the starting acids or esters are 
volatile. However, due to the need to vaporize the starting material the 
pressure is practically limited to about several atmospheres. 
With the vapor phase reaction, the temperature of pyrolysis should be 
sufficiently high to allow the reaction to proceed at a reasonable rate 
and attain good conversion rates. The temperature should also be 
sufficient to completely vaporize the ketal or alpha-enol ether or ester 
of the alpha-acetyl cinnamic acid or ester thereof. In most cases, this is 
accomplished by using a reactor temperature of about 470.degree. to 
530.degree. C. Except when operating under high vacuum, these temperatures 
lead to reaction products in which all of the starting alpha-acetyl 
cinnamic acid ketal, or enol ether or ester, or the ester thereof have 
been consumed. The best conditions are those that favor rapid 
vaporization. Thus, the lowest possible pressure should be employed. 
Industrially, this implies pressures of about 10 mmHg to 60 mmHg since 
these are generally regarded as the lowest pressures which are 
economically attainable. However, in the case of more highly valued 
products, even lower pressures may be used to some advantage. Higher 
pressures than those described above may also be employed, particularly in 
the case where the starting ketal or enol ether or ester are volatile. At 
temperatures below 470.degree. C., the alpha-acetyl cinnamic acid ketal or 
ester thereof or the related enol ether or ester are about 60% to 70% 
consumed. Thus, significantly lower temperatures are suitable, 
particularly if the starting materials are recycled to increase the yield. 
The lower temperatures are also suitable if contact times with the hot 
zone in a chamber are lengthened. Since this reaction is usually performed 
using an inert gas to promote the movement through the tube, this is 
readily obtainable. A simple reduction at the rate of flow of the gas will 
increase the contact tie. 
When the thermal ring closure is conducted in a liquid phase, an inert 
solvent is utilized. 
Within the context of this invention as inert solvent is defined as a 
solvent which can withstand the high reaction temperatures involved in the 
cyclization process without undergoing significant decomposition and which 
does not react with either the starting material or the product. Any high 
normal boiling point solvent fitting this criteria may be utilized as the 
inert solvent at atmospheric pressure. Lower normal boiling point solvents 
can be used if the reaction is conducted under pressure, i.e., in an 
autoclave, thereby attaining the desired temperature while preserving the 
solvent in the liquid phase. When the process is conducted in the liquid 
phase it is typically done so at a temperature of about 175.degree. to 
300.degree. C., and preferably at about 200.degree. to 250.degree. C. The 
inert solvent must have a normal boiling point equal to or greater than 
the reaction temperature for the reaction to proceed at atmospheric 
pressure, or as already indicated if its normal boiling point is lower 
then the reaction must be conducted at supraatmospheric pressure. Examples 
of inert solvents are aromatic solvents including heteroaromatic and 
polycyclic aromatic solvents. alkylated aromatic solvents and halogenated 
aromatic solvents, saturated cyclic and acyclic hydrocarbons, organic 
esters including alkyl, phenyl and benzyl esters, and organic ethers 
including diphenyl ether, among others. More specific examples are methyl 
and t-butyl esters, decalin, 1-methylnaphthalene, naphthalene and 
biphenyl. Other suitable inert solvents may also be used including 
ketones, halogenated aliphatic hydrocarbons aliphatic esters and alcohols, 
among many others. Solvents which should be avoided since they are not 
within the above definition of an inert solvent include olefins, primary 
and secondary amines and carboxylic acids. 
Typically, when the cyclization reaction is conducted in the liquid phase, 
the concentration of the alpha-enol ether or ester or the ketal of the 
alpha-acetyl cinnamic acid or the ester thereof in the solvent may be 
varied over a broad range. Typically, the ketal or alpha-enol ether or 
ester is present in an amount of about 0.01 moles to 1 moles per liter of 
the solvent. 
Suitable R.sup.1 groups in the structures of the compounds illustrated and 
discussed above include H; alkyl groups such as methyl, ethyl, propyl, 
butyl, pentyl, hexyl, decyl, and the like; aryl groups such as phenyl, 
naphthyl, and the like; alkyaryl such as tolyl, anthryl, and the like; 
arslkyl such as benzyl, phenylethyl, phenylpropyl, phenylbutyl, and the 
like. 
Illustrative of suitable R.sup.2 groups in the structures are methyl, 
ethyl, propyl, butyl, pentyl, hexyl, decyl, and the like, and examples of 
suitable R.sup.2 groups in the ketal (I) when taken together are ethylene, 
trimethylene, tetramethylene, and the like. 
Exemplary of R.sup.3 groups are hydrogen, halo such as chloro, bromo and 
fluoro; carboxy; alkyl such as described for R.sup.1 and R.sup.2 ; alkoxy 
such as methoxy, ethyoxy, propoxy, butoxy, pentoxy, and the like; acyl 
such as ethanoly, propanoyl, butanoyl, pentanoyl and the like; acyloxy 
such as ethanoyloxy, propanoyloxy, butanoyloxy, pentanoyloxy, and the 
like; carbalkoxy such as methoxycarbonyl, ethyoxycarbonyl, 
propoxycarbonyl, butoxycarbonyl, etc.; alkylthio such as methylthio, 
ethylthio, propylthio, butylthio, pentylthio, etc. 
Also, the aromatic ring of the alpha-vinyl cinnamic acid or ester thereof 
may be substituted at any position, although preferred positions are the 
ortho and para positions of the ring with respect to the 
carboxy-containing residue. If the ring substitution is in either the para 
or ortho position, the products are entirely predictable. More 
specifically, para-substituted ketals or enol-ethers of alpha-acetyl 
cinnamic acids or esters thereof undergo ring closure to yield 
6-substituted 2-naphthanoates and ortho-substituted alpha-acetyl 
cinnamates yield 8-substituted 2-naphthanoates. On the other hand, the 
meta-substitution of the aromatic ring of the cinnamic acid or ester 
thereof leads to a mixtures of the isomeric 5- and 7-methoxy substituted 
2-naphthanoates, e.g., with the latter predominating slightly in the case 
of the methyl m-methoxy alpha-acetyl cinnamate ketal or enol ether. 
Clearly, the present invention enables the preparation of these unique 
compounds, although they are not obtainable in a form which is 
substantially free of other isomers. 
Although the R.sup.1 substituent of the cinnamic acid ester may be derived 
form an alkyl or aryl group, the methyl ester is preferred due to its high 
volatility, particularly when the cyclization step is conducted in the 
vapor phase. The selection of the specific ester derivative is of lesser 
importance when the reaction is conducted in the liquid phase, and 
therefore there is more latitude in the choice of the specific ester 
utilized. 
Enol ethers of alpha-acetyl cinnamic acids or the esters thereof can be 
obtained by heating the related ketals at a temperature of about 
25.degree. to 300.degree. C., preferably 75.degree. to 250.degree. C. and 
more preferably above 125.degree. C. or by distilling the ketal. Enol 
ethers of alpha-acetyl cinnamic acids or esters thereof can also be 
prepared by other methods known in the art. 
In one particular embodiment of the invention, the heating step producing 
the cyclization of the ketal of a substituted alpha-acetyl cinnamic acid 
or ester thereof is heated at the above temperatures to produce the 
related alpha-enol ether of the alpha-acetyl cinnamic acid or ester 
thereof, and then the thus obtained alpha-enol ether of the alpha-acetyl 
acid cinnamic or ester thereof is heated at a temperature effective to 
cyclize said enol ether to form the substituted 2-naphthanoic acid or 
ester thereof. When the cyclization of the alpha-enol ether of the 
alpha-acetyl cinnamic ester thereof is conducted in the vapor phase, it is 
preferably done at a temperature of about 150.degree. to 800.degree. C., 
and more preferably about 350.degree. to 600.degree. C., and a pressure of 
about 0.001 mmHg to 3 atm, and more preferably about 0.1 mmHg to 
atmospheric pressure. However, much higher temperatures can also be used 
without difficulty, such as temperatures in excess of about 800.degree. C. 
More commonly, the conditions under which the cyclization of the 
alpha-enol ether cinnamic acid or ester thereof is conducted are similar 
to the conditions described above for the cyclization of the related 
ketal. It should be noted that the conversion of the ketal to the cyclic 
product proceeded through the formation of an alpha-enolic structure. 
When the thermal ring closure of the alpha-enol ether cinnamic acid or 
ester thereof is conducted in a liquid phase, an inert solvent is 
utilized. Typically, solvents as those described above for the similar 
reaction of the related ketal are useful in this case. When the process is 
conducted in a liquid phase, it is preferably done at a temperature of 
about 175.degree. to 300.degree. C., and more preferably about 200.degree. 
to 250.degree. C. Similar conditions are also suitable for the cyclization 
of the alpha-enol ester of cinnamic acid or ester thereof. Up to the 
present time the prior art has not addressed in general, or by means of 
examples, the ring closure of ketals of alpha-acetyl cinnamates to 
generate 2-naphthanoates. Furthermore, not even instances of simpler 
benzalacetone ketals being used to generate a naphthalane are known. 
In another aspect of the invention, the 2-naphthanoic acids or esters 
thereof are prepared from an alpha-acetyl cinnamic acid or ester thereof 
of the formula defined above and a ketalizing agent, and the thus obtained 
ketal is then cyclized by heating. 
A number of methods for the ketalization of ketones are known (Gasparrini, 
F., Giovannoli, M., and Misiti, D., Tetrahedron 40:1491 (1984) and 
references cited therein). However, no known applications of these methods 
to alpha-acetyl cinnamic acid or esters thereof are known. 
The ketal of the substituted alpha-acetyl cinnamic acid or ester thereof 
may be obtained by reacting an alpha-acetyl cinnamic acid or ester thereof 
with a ketalizing agent. Suitable ketalizing agents are alkyl glycols and 
dialkyl acetals, dialkyl ketals, and tri-alkyl orthoesters such as 
(C.sub.2 -C.sub.12)glycols, e.g., 1,2- or 1,3-glycols, (C.sub.1 
-C.sub.12)alkyl orthoesters and (C.sub.1 -C.sub.12)dialkyl-ketals or 
acetals derived from (C.sub.1 -C.sub.12)ketones or aldehydes, 
respectively. Examples of suitable glycols and orthoformates are neopentyl 
glycol, propanediol, 1,2- and 1,3-ethylene glycol, trimethyl orthoformate 
and the like. Preferred are alkyl glycols and alkyl orthoformates having 1 
to 5 carbon atoms. Alkyl glycols and di- and tri-alkyl orthoformates are 
commercially available or may be prepared by methods known in the art 
which need not be described herein. 
The reaction of an alpha-acetyl cinnamic acid or ester thereof with a 
ketalizing agent is preferably conducted at a temperature of about 
25.degree. to 250.degree. C., and more preferably about 40.degree. to 
200.degree. C. Typically, this reaction is conducted at atmospheric 
pressure. However, other pressures are also suitable. 
In a still more preferred embodiment of the invention, the reaction of the 
alpha-acetyl cinnamic acid or ester thereof with the ketalizing agent is 
conducted in the presence of a transition metal catalyst and an acid 
catalyst. Preferred are strong acids such as sulfuric acid, 
trifluoroacetic acid, hydrochloric acid or sulfonic acid or an acidic 
resin such as as acid-exchange resin. Acidic resins are commercially 
available or can be prepared by methods known in the art which need not be 
described herein. A preferred acid resin is Amberlyst-15.RTM.. The 
transition metal catalyst for the ketalization reaction of the invention 
can be any transition metal olefin isomerization catalyst which isomerizes 
the unreacted isomer of the ketone reactant into a more reactive isomer 
and thereby provides a constant supply of reactive ketone. Preferred 
isomerization catalysts are Group VIII metal catalysts, e.g., rhodium, 
ruthenium, cobalt and palladium catalysts and derivatives thereof such as 
cobalt hydrides, and palladium hydrides, among others. Particularly 
preferred among the transition metal catalysts are carbonylhydride 
tris(triphenylphosphine)rhodium and hydridochlorocarbonyl 
tris(triphenylphosphine) ruthenium. The transition metal catalyst will 
always be used in catalytic amounts which usually fall in the range of 
0.01 to 0.001 mole/mole of .alpha.-acetyl cinnamate acid or ester. The 
proportion of the acid catalyst to transition metal catalyst generally 
ranges from about 10:1 to 10,000:1, and more preferably 50:1 to 5,000:1 by 
weight. 
In the reaction of the substituted alpha-acetyl cinnamic acid or ester 
thereof to ketalizing agent may vary widely but ordinarily fall in the 
range of about 1:1 to 1:5 molar equivalents, preferably about 1:1 to 1:3 
molar equivalents. The reaction temperatures employed are those sufficient 
to effect the ketalization reaction and normally fall in the range of 
about 25.degree. to 250.degree. C., preferably about 40.degree. to 
200.degree. C. The reaction proceeds readily at atmospheric pressure but 
the reaction can be conducted under pressure if desired. 
The ketalization reaction is generally conducted in a liquid phase and an 
inert solvent may be added. Within the context of this invention, an inert 
solvent is defined as a solvent which can withstand the reaction 
temperatures involved in the ketalization reaction without undergoing 
significant decomposition and without detracting from the formation of the 
product. Examples of inert solvents are acyclic, cyclic and aromatic 
hydrocarbons, halides thereof or their azeotropes formed with water, 
alcohols and glycols from which the alkylene and alkyl residues of the 
R.sup.2 substituents of the ketals are derived. A preferred group of 
solvents are alcohols or glycols such as methanol, ethanol, and ethylene 
glycol. 
Alpha-acetyl cinnamic acid or ester thereof may be obtained by reacting a 
compound such as acetoacetic acid or an ester thereof of the formula 
CH.sub.3 --CO--CH.sub.2 COOR.sup.1 wherein R.sup.1 is an defined above or 
acetylacetone with a benzaldehyde substituted with R.sup.3, wherein 
R.sup.3 is as defined above. The Knoevenagel condensation of aromatic 
aldehydes and acetoacetic esters is a well known and efficient process for 
generating alpha-acetyl cinnamic acid esters (Jones, Org. Reactions 15:204 
(1967), the content of which is incorporated herein by reference). The 
reaction of acetoacetone with a substituted aromatic benzaldehyde can also 
be conducted under conditions similar to those of the Knoevenagel 
reaction. 
In general, the reaction of acetoacetic acid or an ester thereof or the 
acetylacetone with the benzaldehyde is conducted at a temperature of about 
0.degree. to 250.degree. C., and more preferably about 50.degree. to 
150.degree. C., and at a pressure of about 0.1 mmHg to 10 atm, preferably 
1 atm. In this reaction, the acetoacetic acid or ester thereof or the 
acetylacetone and the benzaldehyde are preferably present in a proportion 
of about 25:1 to 1:25, and more preferably about 1:1 to 1:2 by weight. 
In an alternative embodiment of the invention where the transition metal 
catalyst is not included, the process of the invention may be conducted by 
utilizing a trailkyl orthoformate and an alpha-acetyl cinnamic acid or 
ester thereof in the presence of a solvent and an acidic resin raising the 
temperature beyond the temperatures specified above. The reaction can be 
conducted while maintaining a continuous nert gas purge to remove the 
by-product alkyl ester as it is formed. This procedure yields the ketal 
after several hours. This embodiment is available for the formation of 
di-alkyl ketals, the thus formed ketals are obtained with a high yield, in 
excess of 80 weight percent. 
Cyclic ketals such as those generated by ketalizing with vicinal glycols 
are also useful in this process. Those ketals are generally generated in 
the prior art by treating a ketone with an excess of the glycol in the 
presence of an acidic catalyst while water produced by the reaction is 
continuously removed. However, this prior art method is not applicable to 
the synthesis of the present ketals of alpha-acetyl cinnamic acids or 
esters thereof. In the case of the cyclic ketals, there is no alternative 
to including a transition metal catalyst as described above if high yields 
and conversions are desired. In the case of the cyclic ketals raising the 
temperatures will not make the reaction proceed. 
The cyclization of the ketals or alpha-enol ethers or esters of the 
invention to obtain 2-naphthanoic acids or esters thereof proceeds with a 
crude yield of at least about 70 weight percent to 85 weight percent and 
the product is obtained with a purity generally in the range of 80 weight 
percent to 90 weight percent. 
The substituted 2-naphthanoic acid may be purified by any of a number of 
standard methods, including chromatography, distillation or 
crystallization, among others. After purification, the yield of the 
substituted 2-naphthanoic acid based on the amount of starting 
alpha-acetyl cinnamic acid or ester thereof is greater than about 24 mole 
percent to 65 mole percent, depending on the nature of the substituent on 
the aromatic ring of the starting alpha-acetyl cinnamic acid or ester 
thereof.

Having now generally described this invention, the same will be better 
understood by reference to certain specific examples, which are included 
herein for purposes of illustration only and are not intended to be 
limiting of the invention or any embodiment thereof, unless so specified. 
EXAMPLES 
In all the examples listed below the intermediate ketals are identified on 
the basis of their proton NMR, infrared (IR), and mass spectra including 
an exact mass for the molecular ion. The final 2-naphthanoic products are 
identified on the basis of their proton NMR, IR, and mass spectra. 
EXAMPLE 1 
Ketalization-Cyclization With Acidic Resin and Catalyst 
A solution is prepared in a 50-mL flask containing 10.20 grams (0.050 
moles) of methyl alpha-acetyl cinnamate and 10 milligrams (11 micromoles) 
of hydridocarbonyl (tris-triphenyl-phosphine)rhodium in 30 mL of 1/1 
trimethyl orthoformate/methanol. To this solution are added 1 to 1.2 grams 
of an acid resin, e.g., Amberlyst-15, and the mixture is stirred at room 
temperature for 5 to 16 hours. The reaction is 98% complete in 5 to 7 
hours. Longer reaction times are generally allowed more out of convenience 
than necessity. 
The reaction mixture is then filtered to remove the resin, swirled with 1 
gram of a slightly basic resin, e.g., Amberlyst-21, filtered again, washed 
with 1/1 trimethyl orthoformate/methanol, and the solvent removed in 
vacuo. A sample is examined spectroscopically (NMR, IR, mass spectra) to 
confirm the identity of the ketal. The crude product is a ketal weighing 
12.84 grams. A small amount of enol ether is also present, whose identity 
is also confirmed by mass spectroscopy. 
The crude ketal (8.76 grams, 0.035 moles if the ketal is pure) is pyrolyzed 
using a simple drip-type pyrolysis unit which consisted of a 1 inch 
diameter quartz tube, filled with 20 cm of fine chips, e.g., Vycor.RTM. 
chips, and placed in a 12 inch electric furnace. A thermal couple is used 
to monitor temperature and a furnace is used to maintain the temperature 
between 475.degree. to 495.degree. C. The movement of the material through 
the tube is promoted by an inert gas purge (50 mL/hour) and the crude, 
liquid ketal is added at a rate of 2 mL/hour. This procedure results in 
5.78 grams of crude methyl 2-naphthanoate which is purified 
chromatographically to give 3.80 grams (0.0204 moles) of pure methyl 
2-napthanoate. This represents a yield of 60% from the starting methyl 
alpha-acetyl cinnamate. 
EXAMPLE 2 
Ketalization-Cyclization Without Catalyst 
This exemplifies a ketalization-cyclization in which the ketal is generated 
in the absence of a transition metal catalyst. 
A solution of methyl p-bromo alpha-acetyl cinnamate (mixture of olefin 
isomers, 14.15 grams, 0.050 moles), 15 mL trimethyl orthoformate and 15 mL 
of methanol is prepared in a 50-mL, round-bottom flask equipped with a 
thermometer inlet, a gas inlet consisting of a pipette connected to a 
nitrogen source and supported in a thermometer adaptor and a gas outlet. 
To this solution are added 1.2 grams of an acidic resin, e.g., 
Amberlyst-15, and a slow, consistent inert gas purge is established 
through the solution. The solution is stirred magnetically and maintained 
at a temperature of 55.degree. C. for a period of 5.5 hours. The material 
is then filtered, neutralized by swirling the mixture with a slightly 
basic resin, e.g., Amberlyst-21, and the solvent is removed in vacuo. The 
crude ketal, whose identity is verified spectroscopically, weights 16.42 
grams. 
A sample of the crude ketal (13.30 grams) is pyrolyzed as described in 
Example 1 to give 4.80 grams of methyl 6-bromo-2-naphthanoate after 
recrystallization from methanol. This represents an overall yield of 45% 
from the starting methyl p-bromo-alpha-acetyl cinnamate. 
EXAMPLE 3 
Following the procedure in Example 1, methyl 6-isopropyl 2-naphthanoate is 
obtained with a 63% overall yield from methyl p-isopropyl-alpha-acetyl 
cinnamate. 
EXAMPLE 4 
Following the procedure in Example 1, with the exception that the final 
product is isolated by crystallization from methanol, methyl 6-methyl 
2-naphthanoate is obtained with a 53% yield from methyl p-methyl 
alpha-acetyl cinnamate. 
EXAMPLE 5 
Following the procedure in Example 2, with the exception that the 
intermediate ketal is isolated by crystallization with an 85% yield, 
methyl p-carbomethoxy alpha-acetyl cinnamate is converted to 
2,6-maphthalene dicarboxylic acid dimethyl ester with an overall yield of 
42%. (Yield soley for pyrolysis=49%) 
EXAMPLE 6 
Following the procedure in Example 1, methyl p-methoxy alpha-acetyl 
cinnamate is converted to methyl 6-methoxy 2-naphthanoate with a yield of 
27%. 
EXAMPLE 7 
Following the procedure in Example 1, methyl o-methoxy alpha-acetyl 
cinnamate is converted with a 34% yield to methyl 
8-methoxy-2-naphthanoate. 
EXAMPLE 8 
Following the procedure in Example 1, methyl m-methoxy alpha-acetyl 
cinnamate is converted to a mixture of 5- and 7-methoxy substituted 
2-naphthanoic acid methyl esters which are obtained in yields of 19% and 
24%, respectively. 
EXAMPLE 9 
Enolization-Cyclization Without catalyst 
This example demonstrates the utility of the enol ethers in the 
cyclization. 
A crude dimethyl ketal of methyl p-methyl alpha-acetyl cinnamate is 
generated as in Example 2 and then instead of pyrolyzing the material 
directly, it is distilled at 0.5 to 1.5 mmHg (bp: 125.degree. to 
130.degree. C.). The NMR spectrum of the product indicates that the 
compound is a 1:1 mixture of the olefinic isomers of the methyl enol ether 
of methyl p-methyl alpha-acetyl cinnamate contaminated with about 10% of 
the related ketal. The enol ether is pyrolyzed as in Example 1 to give a 
69% yield of methyl 6-methyl 2-naphthanoate as calculated from the enol 
ether. 
EXAMPLE 10 
This example demonstrates the feasibility of operating the reaction in the 
liquid phase. A 1.02 gram (3.86 mmol) sample of crude methyl p-methyl 
alpha-acetyl cinnamate dimethyl ketal, is generated as described in 
Example 2, dissolved in 51 mL of 1-methyl naphthalene and heated at reflux 
for 6 hours. The reaction mixture is added to a chromatography column and 
eluted first with hexane until no more 1-methylnaphthalene is detectable 
in the hexane fractions. The product is then obtained by further eluting 
the material with 5% ethyl acetate in hexane to give 0.330 grams (1.65 
mmol, 43%) of pure methyl 6-methyl 2-naphthanoate. 
EXAMPLE 11 
Cyclic Ketalization-Cyclization 
This example demonstrates the feasibility of using cyclic ketals in this 
process. 
The ethylene glycol ketal of methyl p-methyl alpha-acetyl cinnamate is 
prepared as follows. To a 500-mL, three-neck flask equipped with a 
Dean-Stark trap are added methyl alpha-acetyl-4-methylcinnamate (51 grams; 
0.234 mol), ethylene glycol (50 grams; 0.806 mol), carbonylhydrido 
tris(triphenylphosphine) rhodium (0.250 gram; 0.27 mol), an acidic resin, 
e.g., Amberlyst-15 (1.00 gram) and cyclohexane (150 mL). The mixture is 
heated at reflux for 5.5 hours while the water of reaction is collected. 
When 20 mL of the ethylene glycol/water layer are collected in the 
Dean-Stark trap, it is removed from the trap and an additional 20 mL of 
dry ethylene glycol is added to the reaction mixture. The mixture is 
sampled periodically and analyzed by GC and H NMR. The initial ratio of 
the Z isomer to the E isomer is 1.3:1.0. This ratio remained essentially 
constant throughout the reaction. After 5 hours the ketone is about 90% 
converted to the ethylene ketal. Of the unconverted ketone, the ratio of Z 
to E isomers as determined from the H NMR spectrum is still about 1.3:1. 
A sample of this ketal (3.10 grams, 11.8 mmol) is pyrolyzed as described in 
Example 1 to generate 2.09 grams of crude methyl 6-methyl alpha-acetyl 
cinnamate which is about 77% pure by gas chromataographic assay. 
EXAMPLE 12 
Reduced Pressure 
This example demonstrates the feasibility of running this process under 
reduced pressures. 
A toluene solution of 40.0 grams of the dimethyl ketal of methyl 
p-carbomethoxy alpha-acetyl cinnamate is generated as in Example 5, 
pyrolyzed using a flash pyrolysis unit whose flash evaporation section 
consisted of a 300-mL, three-necked, round-bottom flask which is filled 
about 33% full with coarse chips, e.g., Vycor.RTM. chips and fitted with a 
thermocouple well in one neck, an addition funnel containing the solution 
in the second neck and an outlet to the pyrolysis unit in the third neck. 
The pyrolysis unit is identical to the unit described in Example 1 except 
that the outlet end of the unit is now connected to a vacuum line. The 
temperature in the pyrolysis unit is maintained at 490.degree. C. and the 
vacuum set initially at 0.5 mmHg. 
The flash unit is heated to 300.degree. C. and the addition of the ketal 
solution is initiated. The rate of addition of the ketal solution is slow 
enough to maintain the temperature in the flash unit and to allow the 
pressure to return to nearly the desired level between drops. This takes 
nearly an hour. The resultant product weighs 30.0 grams and its assay by 
gas chromatography indicates that the product contains 5.1 grams of the 
desired 2,6-naphthalene dicarboxylic acid dimethyl ester. The remaining 
materials consist of the corresponding enol ethers and the intermediate 
dihydronaphthalene which are the expected intermediates in the conversion. 
This finding is supported by gas chromatography-mass spectral analysis. 
Considering these intermediates as starting material equivalents, this 
represents a yield of 53% and a conversion of 31%. 
The invention now being fully described, it will be apparent to one of 
ordinary skill in the art that many changes and modifications can be made 
thereto without departing from the spirit or scope of the invention as set 
forth herein.