Isopropyl- and isopropenyl cyclopentene carboxylic esters

#This invention relates to the field of fragrance.

#The cyclopentenes involved in this invention have the following general formula ##STR1## wherein R.sup.1 represents a hydrogen atom or a hydroxy, lower alkyl or lower alkoxy group, R.sup.2 represents a hydrogen atom or a lower alkyl or lower alkylidene group and the broken line denotes an optional bond.

#As aforesaid, the cyclopentenes manufactured according to the present invention have the following general formula ##STR2## wherein R.sup.1 represents a hydrogen atom or a hydroxy, lower alkyl or lower alkoxy group, R.sup.2 represents a hydrogen atom or a lower alkyl or lower alkylidene group and the broken line denotes an optional bond.

#The following Examples illustrate the process provided by the present invention.

#15 drops of 85% phosphoric acid were added to a mixture, cooled in a laboratory autoclave, of 76 g of 3-isopropenyl-1-methyl-2-methylene-cyclopentan-1-ol and 120 g of isopropenyl methyl ether. After gassing with nitrogen, the autoclave was brought, in an oil bath of 180.degree. C, to an internal temperature of 150.degree. C and held at this temperature until a distinct drop in pressure occurred (about 50-75 minutes). The reaction mixture was quenched by intensive cooling, treated with solid potassium hydroxide and concentrated under reduced pressure on a rotary evaporator. By fractional distillation over solid potassium hydroxide there were obtained 58 g (60%) of 3-isopropenyl-1-methyl-2-(3-oxobutyl)-cyclopent-1-ene; boiling point .sub.0.01 = 69.degree.-72.degree. C; N.sub.D.sup.20 = 1.4836. The compound has a woody, camphoraceous, ionone-like fragrance.

#4 g of 3-isopropenyl-1-methyl-2-(3-oxobutyl)-cyclopent-1-ene were hydrogenated in 50 ml of ethyl acetate in the presence of 400 mg of palladium on calcium carbonate (5%). After the uptake of one equivalent of hydrogen, the solution was filtered over Celite, concentrated and distilled under a high vacuum. There were obtained 4 g of 3-isopropyl-1-methyl-2-(3-oxobutyl)-cyclopent-1-ene; boiling point .sub.0.005 about 70.degree. C; n.sub.D.sup.20 = 1.4709; IR.sub.film : .nu..sub.max = 1.725, 1390/70 and 1170 cm.sup.-1. The compound has a woody, floral note.