Patent GB-733805-A (GB)
Title: Substituted dihydropyrans
IPC: C07D309/30
Filed: 1952-11-24
Abstract: The invention comprises dihydropyrans of the general formula <FORM:0733805/IV (b)/1> wherein R1 and R2 represent hydrogen or methyl groups, R and R4 are hydrocarbon groups which are free from non-benzenoid unsaturation and contain from 1 to 12 carbon atoms, and R3 is a hydrocarbon group which is free from non-benzenoid unsaturation and contains from 1 to 18 carbon atoms, and the preparation thereof by heating an olefinic ester having the general formula R-CO-CR1=CR2-COOR3 with a vinyl ether having the general formula R4OCH=CH2, R, R1, R2, R3 and R4\h having the above significance.  The preferred dihydropyrans are alkyl 2-alkoxy-6-alkyl-3,4-dihydro-1,2-pyran-4-carboxylates in which each alkyl and alkoxy group contains from 1 to 12 carbon atoms, and alkyl 2-aryloxy-6-alkyl-3,4-dihydro-1,2-pyran-4-carboxylates in which each alkyl group contains from 1 to 12 carbon atoms and the aryloxy group contains from 6 to 10 carbon atoms.  The process may be carried out at a temperature from 100 DEG  to 300 DEG  C., and the reaction mixture may contain an excess of the vinyl ether reactant.  The carboxylic ester group in the compounds of the above general formula may be hydrolysed with dilute alcoholic alkali to form alkali metal salts, e.g. sodium and potassium salts, and then acidifying with a mineral or a strong organic acid to form compounds of the above general formula wherein R3 represents hydrogen.  Polymerization inhibitors such as hydroquinone, pyrogallol, b -naphthol and 2,5-di-tertiary-butyl-hydroquinone may be present in the reaction mixture.  Suitable olefinic esters which may be used in the above process are b -aroylacrylates in which the aroyl group has 7 to 11 carbon atoms such as ethyl, dodecyl, phenyl and 4-ethylphenyl b -benzoyl acrylates and b -(2-naphthyl) acrylates, b -acylacrylates in which the acyl group has from 2 to 11 carbon atoms such as methyl, amyl, hexadecyl, phenyl, 4-tolyl and cyclohexyl b -acetyl, b -butyryl and b -lauroyl acrylates, the b -acyl- and b -aroyl-methacrylates such as methyl and phenyl b -acetyl- and b -benzoyl-methacrylates, the b -acyl- and b -aroyl-tiglates such as isopropyl and cyclopentyl b -propionyl- and b -benzoyl-tiglates, the b -acylangelates such as methyl b  - acetylangelate, and the b  - acyldimethylacrylates such as amyl b -benzoyl-a ,b -dimethylacrylate.  Examples of suitable vinyl ether reactants are alkyl vinyl ethers such as methyl, isobutyl, hexyl and dodecyl vinyl ethers, the cycloalkyl vinyl ethers such as cyclohexyl or a methyl-cyclopentyl vinyl ether, the aryl vinyl ethers having from 6 to 10 carbon atoms in the aryl group such as phenyl or a naphthyl vinyl ether, the alkaryl vinyl ethers such as 4-butylphenyl or a xylyl vinyl ether, and the aralkyl vinyl ethers such as 2-phenylethyl and b -naphthylmethyl vinyl ether.  In the examples the following compounds are prepared:-methyl 2 - ethoxy - 6 - methyl - 3,4 - dihydro - 1,2 - pyran-4-carboxylate and the corresponding 6-phenyl substituted compound.  Other compounds referred to are isobutyl 6-ethyl-2-lauryloxy - 3,4 - dihydro - 1,2 - pyran - 4 - carboxylate, ethyl 2 - ethoxy - 5 - methyl - 6 - ethyl-3,4 - dihydro - 1,2 - pyran - 4 - carboxylate and methyl 2 - phenoxy - 6 - phenyl - 3,4 - dihydro - 1,2-pyran-4-carboxylate.