STEREODIRECTED SYNTHESIS OF (Е)- AND (Z)-ISOMERS OF 8-CHLOROOCT-7-EN-4-ONE

Abstract

For citation:Shakhmaev R.N., Sunagatullina A.Sh., Alieva R.M., Zorin V.V. Stereodirected synthesis of (Е)- and (Z)-isomers of 8-chlorooct-7-en-4-one. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 40-44. Reaction of ethyl 3-oxohexanoate with equimolar amounts of (E)- or (Z)-1,3-dichloro-propene under phase transfer catalysis conditions in the presence of K2CO3 afforded the corresponding monosubstituted (E)- or (Z)-isomers of ethyl 2-(3- chloroprop-2-en-1-yl)-3-oxohexa-noate and considerable amount of disubstituted derivatives (30-40%). In order to increase yields of monosubstituted derivatives we carried out research to test the known methods of selective monoalkylation of β-dicarbonyl compounds with respect to test substrates. Alkylation of ethyl 3-oxohexanoate in the presence of tetrabutylammonium fluoride and cobalt salts have not led to a significant increase in reaction selectivity, but in the reaction in solid in the absence of solvent the formation of disubstituted products is not practically observed. In the reaction of ethyl 3-oxo-hexanoate with (E)- or (Z)-isomers of 1,3-dichloropropene on the surface of Al2O3 impregnated with t-BuOK monosubstituted products are formed with the yields of 81 and 79%, respectively. Solid phase alkylation proceeds with high stereoselectivity, isomeric purity of target products are greater than 99%. Standard methods of monoalkylated ketoesters decarboxylation under acidic or basic conditions lead to low yields of the corresponding chlorovinyl ketones, best results are obtained at decarboxylation of (E)- or (Z)-isomers of ethyl 2-(3-chloroprop-2-en-1-yl)-3-oxohexa-noate in slightly modified Krapcho conditions. Carrying out the reaction in N-metrhylpirroli-dinone at a temperature of 130-140 °C in the presence of 3 eq. LiCl leads to (E)- and (Z)-isomers of 8-chlorooctyl-7-ene-4-one with 81 and 77% yields, respectively, and an isomeric purity of ~ 99%.