SYNTHESIS OF (E)- AND (Z)-ISOMERS OF 2-(3-CHLOROPROP-2-EN-1-YL)CYCLOPENTANONE

Abstract

The possibility of the synthesis of (E)- and (Z)-isomers of 2-(3-chloroprop-2-en-1-yl)cyclopentanone based on allylation of an available ethyl 2-oxocyclopenthanecarboxylate by individual isomers of 1,3-dichloropropene followed by decarboxylation of the resulting isomers of ethyl 1-(3-chloroprop-2-en-1-yl)-2-oxocyclopenthanecarboxylate was investigated. The allylation of ethyl 2-oxocyclopenthanecarboxylate by (E)- or (Z)-isomers of 1,3-dichloropropene under the phase-transfer catalysis conditions in the presence of K2CO3 smoothly leads to the corresponding isomers of ethyl 1-(3-chloroprop-2-en-1-yl)-2-oxocyclopenthanecarboxylate with 84 and 80% yields, respectively. Decarboxylation of alkylated ketoesters under basic conditions leads to ring opening and formation of the corresponding α-substituted adipic acids, and under acid conditions in unacceptably low yields of ketones. Best results are obtained by decarboxylation of isomers of ethyl 1-(3-chloroprop-2-en-1-yl)-2-oxocyclopenthanecarboxylate under Krapcho conditions. However, in this case a side-formation of the corresponding α-substituted mono- and diethyl esters of adipic acid is observed too. The optimization of the reaction showed that the addition of acetic acid as the proton donor suppresses almost completely the ring opening. The decarboxylation in N-methylpyrrolidone at a temperature of 130-150 °C in the presence of 3 eq. LiCl, 2 eq. water and 2 eq. acetic acid affords to (E)- and (Z)-isomeric 2-(3-chloroprop-2-en-1-yl)cyclopentanones with 75-77% yields and stereochemical purity of ~ 99%.Forcitation:Alieva R.M., Sunagatullina A.Sh., Shakhmaev R.N., Zorin V.V. Synthesis of (E)- and (Z)-isomers of 2-(3-chloroprop-2-en-1-yl)cyclopentanone. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 4. P. 21-25.