Pyrazine-2-ylmethyl-ketones and their fungicidal use

A pyrazine compound of the formula: ##STR1## wherein R.sub.1 and R.sub.2 are hydrogen, or optionally-substituted hydrocarbyl, aryloxy or alkoxy and R.sub.2, additionally may be pyridyl, thienyl or furyl; R.sub.3 and R.sub.4 are H, alkyl or aryl or together form a bridging group; Z is: ##STR2## where R.sub.5 is H, alkyl or aryl; and functional derivatives and salts thereof. The compounds are useful for combating fungal or bacterial diseases in plants.

This invention relates to pyrazine compounds useful as pesticides and also 
as plant growth regulating substances, to a process for preparing them, to 
compositions containing them and to a method of combating pests, 
especially fungi and bacteria, using them. 
The invention provides pyrazine compounds having the general formula: 
##STR3## 
wherein R.sub.1 and R.sub.2 are hydrogen, optionally-substituted 
hydrocarbyl, aryloxy or alkoxy and R.sub.2, additionally, may be pyridyl, 
thienyl or furyl; R.sub.3 and R.sub.4 are H, alkyl or aryl or together 
form a bridging group; Z is: 
##STR4## 
where R.sub.5 is H, alkyl or aryl; and functional derivatives and salts 
thereof. 
Functional derivatives are esters, ethers and metal complexes. 
Suitable salts are salts with inorganic or organic acids, e.g. 
hydrochloric, nitric, sulphuric, toluenesulphonic, acetic or oxalic acid. 
The esters are suitably alkanoates (e.g. acetates) and the ethers are 
suitably alkyl (e.g. methyl or ethyl), aryl (e.g. phenyl) or aralkyl (e.g. 
benzyl) ethers. 
The metal complex is suitably one including copper, zinc, manganese or 
iron. 
The compounds of the invention contain chiral centres when R.sub.1 is other 
than hydrogen. The compounds are generally obtained in the form of racemic 
mixtures. However these or other mixtures can be separated into the 
individual isomers by methods known in the art e.g. chromatography. In 
many cases, the compounds can be prepared stereospecifically in the form 
of a single diastereoisomer. 
In a further aspect the invention provides pyrazine compounds having the 
general formula: 
##STR5## 
wherein R.sub.1 and R.sub.2 are hydrogen, or optionally-substituted 
hydrocarbyl, aryloxy or alkoxy; R.sub.3 and R.sub.4 are H, alkyl or aryl 
or together form a bridging group; Z is: 
##STR6## 
where R.sub.5 is H, alkyl or aryl; and functional derivatives and salts 
thereof. 
When R.sub.1 and R.sub.2 are hydrocarbyl groups they are preferably simple 
hydrocarbyl radicals in view of the ready availability of these. It is to 
be understood however that the whole range of hydrocarbyl groups, 
unsubstituted or substituted, is considered to fall within the scope of 
this invention since the particular nature of the hydrocarbyl group, if 
one is present, is not believed to be critically important. Thus the 
hydrocarbyl groups may be saturated or unsaturated, straight or branched 
chain, single-ring or multi-ring; thus R.sub.1 may be, for example, alkyl, 
alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, or alkaryl groups, for 
example methyl, ethyl, propyl, butyl, cyclohexyl, allyl or propynyl 
groups, and one or more of their hydrogen atoms may be substituted by 
simple substituents, such as, for example, halogen atoms, for example 
chlorine, bromine and fluorine, or pseudo halogen groups such as, for 
example cyano, or groups such as amino, hydroxy, nitro, phenyl and 
mercapto groups (which may themselves bear substituents). When R.sub.1, 
R.sub.2, R.sub.3 and R.sub.4 are alkyl groups, or R.sub.1 and R.sub.2 are 
alkoxy groups, preferred alkyl and alkoxy groups are straight or branched 
chain groups having 1 to 4 carbon atoms and especially 3 or 4 carbon 
atoms; examples are methyl, ethyl, propyl (n-, iso- or t-butyl), methoxy 
or ethoxy. Preferred aryl groups or aryloxy groups, for R.sub.1 are phenyl 
and phenoxy groups and halophenyl and halophenoxy groups. Particularly 
preferred aryl or aralkyl groups for R.sub.1 are fluorobenzyl, 
chlorobenzyl, benzyl, fluorophenyl and chlorophenyl. Preferred groups for 
R.sub.2 are branched and straight chain alkyl especially t-butyl, propyl 
and optionally-substituted phenyl especially halo-phenyl. Preferred 
substituents on any phenyl or phenoxy group for R.sub.1 or R.sub.2 are one 
or two halogens, and chlorine and fluorine especially. R.sub.3 and R.sub.4 
are preferably hydrogen but when they together form a bridging group, a 
preferred such group contains 4 carbon atoms. 
In a preferred aspect the invention provides pyrazine compounds having the 
general formula: 
##STR7## 
wherein Z is C.dbd.O or CHOH; R.sub.1 is hydrogen, allyl, C.sub.1 to 
C.sub.4 alkyl especially butyl, phenyl, benzyl, phenoxy, mono- or di-, 
fluoro- or chloro-, -benzyl or -phenoxy; R.sub.2 is C.sub.1 to C.sub.4 
alkyl especially propyl or butyl, phenyl, or halophenyl; and functional 
derivatives and salts thereof. 
In a particularly preferred aspect the invention provides pyrazine 
compounds having the general formula: 
##STR8## 
Z is C.dbd.O or CHOH, R.sub.1 is fluoro-, chloro-, or dichloro-, -phenoxy 
or -benzyl; and R.sub.2 is phenyl, halophenyl, propyl or butyl especially 
t-butyl. 
Examples of the compounds of the invention are shown in Table I, and 
correspond to the general formula: 
##STR9## 
except for Compound No. 28, the full structure of which is set out in the 
Table. 
TABLE 1 
__________________________________________________________________________ 
M.P. OR B.P. 
COMPOUND IN DEGREES 
NO R.sub.1 R.sub.2 R.sub.3 
Z CENTIGRADE 
__________________________________________________________________________ 
1 H t-C.sub.4 H.sub.9 
H CO 74.degree.-76.degree./0.08 mm 
2 
##STR10## 
##STR11## 
H CO 110.degree.-112.degree. 
3 
##STR12## t-C.sub.4 H.sub.9 
H CO 96.degree.-97.degree. 
4 nC.sub.4 H.sub.9 
##STR13## 
H CO 73.degree.-74.degree. 
5 CH.sub.2 . CHCH.sub.2 
t-C.sub.4 H.sub.9 
H CO 100.degree.-110.degree./0.1 mm 
6 
##STR14## t-C.sub.4 H.sub.9 
H CO 94.degree.-96.degree. 
7 
##STR15## 
##STR16## 
H CO 131.degree.-133.degree. 
8 
##STR17## t-C.sub.4 H.sub.9 
H CO 108.degree.-110.degree. 
9 
##STR18## 
##STR19## 
H CH . OH 
114.degree.-117.degree. 
10 
##STR20## t-C.sub.4 H.sub.9 
H CH . OH 
97.degree.-99.degree. 
11 
##STR21## t-C.sub.4 H.sub.9 
H CO 102.degree.-104.degree. 
12 H 
##STR22## 
H CO 83.degree.-85 
13 H 
##STR23## 
H CO 51.degree.-52.degree. 
14 n-C.sub.4 H.sub.9 
##STR24## 
H CO 59.degree.-62.degree. 
15 
##STR25## 
##STR26## 
H CO 135.degree.-136.degree. 
16 
##STR27## 
##STR28## 
H CO 128.degree.-130.degree. 
17 
##STR29## n-C.sub.3 H.sub.7 
H CO 45.degree.-46.degree. 
18 
##STR30## 
##STR31## 
H CO 107.degree.-109.degree. 
19 
##STR32## 
##STR33## 
H CO 116.degree.-118.degree. 
20 
##STR34## t . C.sub.4 H.sub.9 
H CO 85.degree.-87.degree. 
21 
##STR35## 
##STR36## 
H CO 114.degree.-116.degree. 
22 
##STR37## t . C.sub.4 H.sub.9 
H CO oil 
23 
##STR38## n-C.sub.3 H.sub.7 
H CO 62.degree.-64.degree. 
24 
##STR39## t . C.sub.4 H.sub.9 
H CO 90.degree.-100.degree. 
25 
##STR40## t . C.sub.4 H.sub.9 
H CO 51.degree.-53.degree. 
26 
##STR41## t . C.sub.4 H.sub.9 
H CO 76.degree.-78.degree. 
27 
##STR42## t . C.sub.4 H.sub.9 
H CO 93.degree.-95.degree. 
28 
##STR43## 144.degree.-146.degree. 
__________________________________________________________________________ 
in this specification the numbering of the pyrazine ring is as follows: 
##STR44## 
The majority of the pyrazine compounds of the invention may be made by the 
reaction of ketones of the general formula: 
##STR45## 
wherein R.sub.2 is alkyl, aryl, or cycloalkyl with appropriately 
substituted alkyl, aralkyl, or alkenyl halides in the presence of base in 
hydroxylic or non-hydroxylic solvents. The resulting ketones are reduced 
using metal hydrides in a suitable solvent, or by using hydrogen in the 
presence of a suitable catalyst. 
Alternatively the ketones mentioned in this invention could be made by 
alkylating 2-methylpyrazine with appropriately substituted organic halides 
and acylating them using suitable acylating agents. The synthetic sequence 
is depicted as shown below: 
##STR46## 
The .alpha.-aryloxypyrazines may be made by halogenating the aforementioned 
ketones of the formula: 
##STR47## 
and displacing the halogen with an appropriately substituted phenol in the 
presence of a base in a suitable solvent. 
##STR48## 
The salts, metal complexes, ethers and esters of the compounds of general 
formula (I) can be prepared from the latter in known manner. For example, 
the complexes can be made by reacting the uncomplexed compound with a 
metal salt in a suitable solvent. 
The compounds are active fungicides, particularly against the diseases: 
Piricularia oryzae on rice 
Puccinia recondita, Puccinia striiformis and other rusts on wheat, Puccinia 
hordei, Puccinia striiformis and other rusts on barley, and rusts on other 
hosts e.g. coffee, apples, vegetables and ornamental plants 
Plasmopara viticola on vines 
Erysiphe graminis (powdery mildew) on barley and wheat and other powdery 
mildews on various hosts such as Sphaerotheca fuliginea on cucurbits (e.g. 
cucumber), Podosphaera leucotricha on apples and Uncinula necator on vines 
Cercospora arachidicola on peanuts and other Cercospora species on for 
example sugar beet, bananas and soya beans 
Botrytis cinerea (grey mould) on tomatoes, strawberries, vines and other 
hosts 
Phytophthora infestans (blight) on tomatoes and potatoes 
Venturia inaequalis (scab) on apples 
Some of the compounds have also shown a broad range of activities against 
fungi in vitro. They have activity against various post-harvest diseases 
on fruit (e.g. Penicillium digatatum and italicum on oranges and 
Gloeosporium musarum or bananas). Further some of the compounds are active 
as seed dressings against: Fusarium spp., Septoria spp., Tilletia spp. 
(i.e. bunt, a seed borne disease of wheat), Ustilago spp., and Pyrenophora 
spp. on cereals. 
They can also be used as industrial (as opposed to agricultural) 
fungicides, e.g. as paint film fungicides. 
The compounds also have plant growth regulating activities. 
The plant growth regulating effects of the compounds are manifested as for 
example a stunting or dwarfing effect on the vegetative growth of woody 
and herbaceous mono- and di-cotyledonous plants. Such stunting or dwarfing 
may be useful, for example, in cereals and soya bean where reduction in 
stem growth may reduce the risk of lodging. Compounds which induce 
stunting or dwarfing may also be useful in modifying the growth of sugar 
cane thereby increasing the concentration of sugar in the cane at harvest. 
Stunting of peanuts can assist in harvesting. Growth retardation of 
grasses can help maintenance of grass swards. Examples of suitable grasses 
are Stenotaphrum secundatum (St. Augustine grass), Cynosurus cristatus, 
Lolium multiflorum, and perenne, Agrostis tenuis, Cynodon dactylon 
(Bermuda grass), Dactylis glomerata, Festuca spp. (e.g. Festuca rubra) and 
Poa spp. (e.g. Poa pratense). At least some of the compounds will stunt 
grasses without significant phytotoxic effects and without deleteriously 
affecting the appearance (particularly the colour) of the grass; this 
makes such compounds attractive for use on ornamental lawns and on grass 
verges. The compounds can also stunt weed species present in the grasses; 
examples of such weed species are sedges (e.g. Cyperus spp.) and 
dicotyledonous weeds. The growth of non-crop vegetation (e.g. weeds or 
cover vegetation) can be retarded thus assisting in the maintenance of 
plantation and field crops. The plant growth regulating effect may 
manifest itself in an increase in crop yield. 
Other plant growth regulating effects caused by the compounds include 
alteration of leaf angle and promotion of tillering in monocotyledonous 
plants. The former effect may be useful for example in altering the leaf 
orientation of, for example, potato crops thereby letting more light into 
the crops and inducing an increase in phytosynthesis and tuber weight. By 
increasing tillering in monocotyledonous crops (e.g. rice), the number of 
flowering shoots per unit area may be increased thereby increasing the 
overall grain yield of such crops. The treatment of plants with the 
compounds of the invention can lead to the leaves developing a darker 
green colour. 
Further the compounds may inhibit the flowering of sugar beet and thereby 
may increase sugar yield. They may also reduce the size of sugar beet 
without reducing significantly the sugar yield thereby enabling an 
increase in planting density to be made. 
In carrying out the plant growth regulating method of the invention, the 
amount of compound to be applied to regulate the growth of plants will 
depend upon a number of factors, for example the particular compound 
selected for use, and the identity of the plant species whose growth is to 
be regulated. However, in general an application rate of 0.1 to 15, 
preferably 0.1 to 5, kg per hectare is used. However, on certain plants 
even application rates within these ranges may give undesired phytotoxic 
effects. Routine tests may be necessary to determine the best rate of 
application of a specific compound for any specific purpose for which it 
is suitable. 
The compounds also have algicidal, anti-bacterial and anti-viral activities 
as well as herbicidal activity. 
The compounds may be used as such for fungicidal or plant growth regulating 
purposes but are more conveniently formulated into compositions for such 
usage. The invention thus provides also a pesticidal, especially a 
fungicidal, or plant growth regulating, composition comprising a compound 
of general formula (I) or a salt, complex, ether or ester thereof as 
hereinbefore defined, and a carrier or diluent. 
The invention also provides a method of combating fungal diseases in a 
plant, which method comprises applying to the plant, to seed of the plant 
or to the locus of the plant or seed a compound or salt, complex, ether or 
ester thereof as hereinbefore defined. 
It also provides a method of regulating the growth of a plant, which method 
comprises applying to the plant, to seed of the plant or to the locus of 
the plant or seed a compound or salt, complex, ether or ester thereof as 
hereinbefore defined. 
The invention compounds, salts, complexes, ethers and esters can be applied 
in a number of ways, for example they can be formulated or unformulated, 
directly to the foliage of a plant, or they can be applied also to bushes 
and trees, to seeds or to other medium in which plants, bushes or trees 
are growing or are to be planted, or they can be sprayed on, dusted on or 
applied as a cream or paste formulation, or they can be applied as a 
vapour. Application can be to any part of the plant, bush or tree, for 
example to the foliage, stems, branches or roots, or to soil surrounding 
the roots, or to the seed before it is planted. 
The term "plant" as used herein includes seedlings, bushes and trees. 
Furthermore, the fungicidal method of the invention includes preventative, 
protectant, prophylactic and eradicant treatment. 
The compounds are preferably used for agricultural and horticultural 
purposes in the form of a composition. The type of composition used in any 
instance will depend upon the particular purpose envisaged. 
The compositions may be in the form of dusting powders or granules 
comprising the active ingredient and a solid diluent or carrier, for 
example, kaolin, bentonite, kieselguhr, dolomite, calcium carbonate, talc, 
powdered magnesia, Fuller's earth, gypsum, Hewitt's earth, diatomaceous 
earth and China clay. Compositions for dressing seed, for example, may 
comprise an agent (for example a mineral oil) for assisting the adhesion 
of the composition to the seed; alternatively the active ingredient can be 
formulated for seed dressing purposes using an organic solvent (for 
example N-methylpyrrolidone or dimethylformamide). 
The compositions may also be in the form of dispersible powders, granules 
or grains comprising a wetting agent to facilitate the dispersion in 
liquids of the powder or grains which may contain also fillers and 
suspending agents. 
The aqueous dispersions or emulsions may be prepared by dissolving the 
active ingredient(s) in an organic solvent optionally containing wetting, 
dispersing or emulsifying agent(s) and then adding the mixture to water 
which may also contain wetting, dispersing or emulsifying agent(s). 
Suitable organic solvents are ethylene dichloride, isopropyl alcohol, 
propylene glycol, diacetone alcohol, toluene, kerosene, methylnaphthalene, 
the xylenes, trichloroethylene, furfuryl alcohol, tetrahydrofurfuryl 
alcohol, and glycol ethers (e.g. 2-ethoxyethanol and 2-butoxyethanol). 
The compositions to be used as sprays may also be in the form of aerosols 
wherein the formulation is held in a container under pressure in the 
presence of a propellant, e.g. fluorotrichloromethane or 
dichlorodifluoromethane. 
The compounds can be mixed in the dry state with a pyrotechnic mixture to 
form a composition suitable for generating in enclosed spaces a smoke 
containing the compounds. 
Alternatively, the compounds may be used in a microencapsulated form. 
By including suitable additives, for example additives for improving the 
distribution, adhesive power and resistance to rain on treated surfaces, 
the different compositions can be better adapted for various utilities. 
The compounds can be used as mixtures with fertilisers (e.g. nitrogen-, 
potassium- or phosphorus-containing fertilisers). Compositions comprising 
only granules of fertiliser incorporating, for example coated with, the 
compound, are preferred. Such granules suitably contain up to 25% by 
weight of the compound. The invention therefore also provides a fertiliser 
composition comprising the compound of general formula (I) or a salt, 
metal complex, ether or ester complex thereof. 
The compositions may also be in the form of liquid preparations for use as 
dips or sprays which are generally aqueous dispersions or emulsions 
containing the active ingredient in the presence of one or more wetting 
agent(s), dispersing agent(s), emulsifying agent(s) or suspending 
agent(s). These agents can be cationic, anionic or nonionic agents. 
Suitable cationic agents are quaternary ammonium compounds, for example 
cetyltrimethylammonium bromide. 
Suitable anionic agents are soaps, salts of aliphatic monoesters of 
sulphuric acid (for example sodium lauryl sulphate), and salts of 
sulphonated aromatic compounds (for example sodium 
dodecylbenzenesulphonate, sodium, calcium or ammonium lignosulphonate, 
butylnaphthalene sulphonate, and a mixture of sodium diisopropyl- and 
triisopropyl-naphthalene sulphonates). 
Suitable non-ionic agents are the condensation products of ethylene oxide 
with fatty alcohols such as oleyl or cetyl alcohol, or with alkyl phenols 
such as octyl- or nonylphenol and octylcresol. Other non-ionic agents are 
the partial esters derived from long chain fatty acids and hexitol 
anhydrides, the condensation products of the said partial esters with 
ethylene oxide, and the lecithins. Suitable suspending agents are 
hydrophilic colloids (for example polyvinylpyrrolidone and sodium 
carboxymethylcellulose), and the vegetable gums (for example gum acacia 
and gum tragacanth). 
The compositions for use as aqueous dispersions or emulsions are generally 
supplied in the form of a concentrate containing a high proportion of the 
active ingredient(s), the concentrate to be diluted with water before use. 
These concentrates often should be able to withstand storage for prolonged 
periods and after such storage be capable of dilution with water in order 
to form aqueous preparations which remain homogeneous for a sufficient 
time to enable them to be applied by conventional spray equipment. The 
concentrates may conveniently contain up to 95%, suitably 10-85%, for 
example 25-60%, by weight of the active ingredient(s). When diluted to 
form aqueous preparations, such preparations may contain varying amounts 
of the active ingredient(s) depending upon the intended purpose, but an 
aqueous preparation containing 0.0005% or 0.01% to 10% by weight of active 
ingredient(s) may be used. 
The compositions of this invention can comprise also other compound(s) 
having biological activity [e.g. other growth stimulating substances such 
as the gibberellins (e.g. GA.sub.3, GA.sub.4 or GA.sub.7), the auxins 
(e.g. indoleacetic or indolebutyric acid) and the cytokinins (e.g. 
kinetin, diphenylurea, benzimidazole and benzyladenine) and other 
compounds having complementary fungicidal or insecticidal activity], as 
well as stabilising agent(s), for example epoxides (e.g. epichlorhydrin). 
The other fungicidal compound can be one which is capable of combating ear 
diseases of cereals (e.g. wheat) such as Septoria, Gibberella, 
Helminthosporium and the sooty mould complex; examples of such compounds 
are benomyl, cardendazole (BCM) and captafol. 
Alternatively, it can be one which is capable of combating other seed- and 
soil-borne or foliage diseases; examples of such compounds are Maneb and 
Captan.

The following Examples illustrate the invention; the temperatures are given 
in degrees Centigrade (.degree.). 
EXAMPLE 1 
This Example illustrates the preparation of 
1-phenyl-2-pyrazine-2'-yl-3-p-chlorophenylpropane-1-one (Compound 2, Table 
1) of the formula: 
##STR49## 
2-Phenacylpyrazine [J. Am. Chem. Soc., 81, 5159 (1959)] in dry 
dimethylformamide (20 ml) was added to a suspension of sodium hydride 
(35.0 mg) in dimethylformamide (5 ml). The mixture was stirred at room 
temperature for 4 hours and treated with p-chlorobenzyl chloride (2.44 g) 
dissolved in dimethylformamide (5 ml). After stirring for 3 hours at room 
temperature, the reaction mixture was poured into water, the resulting 
yellow solid was filtered off, washed with water, dried and recrystallised 
from ethyl acetate-petroleum ether (60.degree.-80.degree.). 
1-Phenyl-2-pyrazine-2'-yl-3-p-chlorophenylpropane-1-one is obtained as a 
white crystalline solid. 
EXAMPLE 2 
This Example illustrates the preparation of 
1-t-butyl-2-pyrazine-2'-yl-3-p-chlorophenylpropane-1-one (Compound 3, 
Table 1) of the formula: 
##STR50## 
Pyrazine-2-yl-pinacolone [J. Am. Chem. Soc., 81, 5157-9 (1959)] in dry 
dimethylformamide (20 ml) was added to a suspension of sodium hydride [400 
mg (100%)] in dimethylformamide (5 ml). The reaction mixture was stirred 
at room temperature for 4 hours and treated with p-chlorobenzoyl chloride 
(2.74 g) dissolved in dimethyl formamide (5 ml). The reaction mixture was 
stirred for 3 hours at room temperature and poured into water. After 
work-up as described in Example 1, 
1-t-butyl-2-pyrazine-2'-yl-3-p-chlorophenyl-propane-1-one was crystallised 
from petroleum ether (40.degree.-60.degree.). 
Compounds 4, 5, 7, 8 and 11 of Table 1 were made in a similar manner as 
described in Examples 1 and 2 using the appropriate reactants. 
EXAMPLE 3 
This Example illustrates the preparation of 
.alpha.-pivaloyl-.alpha.-p-chlorophenoxy-2-methylpyrazine (Compound 6, 
Table 1) of the formula: 
##STR51## 
Stage I. Preparation of .alpha.-pivaloyl-.alpha.-bromo-2-methylpyrazine. 
Bromine (0.9 ml) dissolved in acetic acid (5 ml) was added dropwise with 
stirring to pyrazine (3 g) in acetic acid (15 ml). The reaction was 
slightly exothermic and the mixture was stirred for 30 minutes and poured 
into water and extracted with ether. The ethereal layer was successively 
washed with water, sodium bicarbonate solution, water and dried 
(MgSO.sub.4) and the solvent was removed to give 
.alpha.-pivaloyl-.alpha.-bromo-2-methylpyrazine as an orange oil which 
solidified on cooling. This was used in the next stage without further 
purification. 
Stage II. 
To a solution of sodium ethoxide [prepared by reacting sodium (270 mg) with 
ethanol (20 ml)] was added p-chlorophenol (1.5 g) with stirring. After 10 
minutes, .alpha.-pivaloyl-.alpha.-bromo-2-methylpyrazine dissolved in 
ethyl acetate (10 ml) was added dropwise at room temperature and the 
reaction mixture was stirred for two hours. The mixture was filtered and 
the filtrate was concentrated in vacuo and diluted with water. The 
solution was extracted with ether and the ethereal layer was washed with 
water, dried (MgSO.sub.4) and the solvent was removed in vacuo. The 
resulting yellow solid (the title compound) was recrystallized from 
petroleum ether (60.degree.-80.degree.). 
EXAMPLE 4 
This Example illustrates the preparation of 
1-phenyl-3-p-chlorophenyl-2-pyrazine-2'-yl-propane-1-ol (Compound 9, Table 
1), having the formula: 
##STR52## 
Sodium borohydride (350 mg) was added to a solution of 
1-phenyl-3-p-chlorophenyl-2-pyrazine-2'-propane-1-one (3.0 g) in methanol 
(30 ml). After the slight exothermic reaction was finished, the reaction 
mixture was refluxed for one hour. The solvent was removed in vacuo, 
hydrochloric acid (40 ml of 1 N) was added when a white solid was 
obtained. This was filtered off, washed with water and dried. The title 
compound was crystallised from ethyl acetate/petroleum ether 
(60.degree.-80.degree.). 
Compound No. 10 in Table 1 is also prepared in a similar manner using the 
appropriate ketone. 
EXAMPLE 5 
This Example lists a number of compositions of the invention. 
(1) Dispersible Powder 
Compound 11 (of Table I)--50% wt/wt 
Aerosol OT--2% 
Polyfon H--5% 
China Clay--43% 
(2) Emulsifiable Concentrate 
Compound 11--100 g/liter 
Amine dodecylbenzene sulphonate--400 g/liter 
2-n-Butoxyethanol--to 1 liter 
(3) Aqueous Suspension 
Compound 11--250 g/liter 
Polyfon H--25 g/liter 
Bentonite--15 
Polysaccharide--0.75 
Water--to 1 liter 
(4) Dust 
Compound 11--5% wt/wt 
China clay--95% 
(5) Granules 
Compound 11--5% wt/wt 
Starch--5% 
China clay--90% 
(6) Solvent solution 
Compound 11--200 g/liter 
Dimethylformamide--to 1 liter 
The other compounds of Table I were similarly formulated. 
EXAMPLE 6 
The pyrazine compounds were tested against a variety of foliar fungal 
diseases of plants. The technique employed was as follows. 
The plants were grown in John Innes Potting Compost (No. 1, or Seed, as 
appropriate) in 4 cm diameter mini-pots. A layer of fine sand was placed 
at the bottom of the pot to facilitate uptake of test compound by the 
roots. Vermiculite was used to cover the seed in the soil tests. 
The test compounds were formulated either by bead-milling with aqueous 
Dispersol T or as a solution in acetone/ethanol which was diluted to the 
required concentration immediately before use. For the foliage diseases, 
100 ppm a.i. suspensions were sprayed on to the foliage and applied to the 
roots of the same plant via the soil. (Sprays were applied to maximum 
retention, and root drenches to a final concentration equivalent to 
approximately 40 ppm a.i./dry soil). Tween 20, to give a final 
concentration of 0.1%, was added when the sprays were applied to the 
cereals. 
For most of the tests, the test compound was applied to the soil (roots) 
and to the foliage (by spraying) one or two days before the plant was 
inoculated with the diseases. An exception was the test on Erysiphe 
graminis, in which the plants were inoculated 24 hours before treatment. 
After inoculation, the plants were put into an appropriate environment to 
allow infection to take place and then incubated until the disease was 
ready for assessment. The period between inoculation and assessment varied 
from 4 to 14 days according to the disease and invironment. 
The disease control was recorded by the following grading: 
4=No disease 
3=0-5% 
2=6-25% 
1=26-60% 
0=&gt;60% 
The results are shown in Table II. 
TABLE 2 
__________________________________________________________________________ 
Puccinia 
Phytophthora 
Plasmopara 
Piricularia 
Botrytis 
Erysiphe 
COMPOUND 
recondita 
infestans 
viticola 
oryzae 
cinerea 
graminis 
NO (wheat) 
(tomato) 
(vine) 
(rice) 
(tomato) 
(barley) 
__________________________________________________________________________ 
1 0 0 0 2 0 4 
2 1 0 0 0 0 4 
3 1 0 0 0 0 4 
4 0 0 -- 0 0 4 
5 1 0 -- 1 1 4 
6 0 0 0 0 0 4 
7 1 1 0 0 0 3 
8 1 2 0 3 4 4 
9 1 2 0 0 4 3 
10 0 0 2 0 2 4 
11 0 0 0 0 1 4 
12 0 0 0 2 0 3 
13 1 0 0 0 2 0 
14 1 0 0 0 2 4 
15 0 0 0 1 1 4 
16 1 1 0 1 0 4 
17 0 1 2 2 0 4 
18 1 0 0 1 3 4 
19 0 0 0 0 2 4 
20 2 0 0 0 2 4 
21 1 0 0 1 3 3 
22 0 0 0 0 0 4 
23 2 0 1 0 0 4 
24 0 0 0 1 2 4 
25 1 3 -- 2 0 4 
26 0 2 -- 3 1 4 
27 1 2 -- 0 1 4 
28 -- -- -- 1 -- 1 
__________________________________________________________________________ 
Compounds Nos 25 and 26 scored gradings of 3 and 4, respectively, against 
the disease Cercospora arachidicola (leaf spot) on peanuts.