PHOSPHONATE REAGENTS FOR THE SYNTHESIS OF ENOL ETHERS AND ONE-CARBON HOMOLOGATION TO ALDEHYDES

Phosphonate reagents 7a, b, d were developed for the preparation of enol ethers 2 (Z = OR) from carbonyl compounds 1. The phosphonates 7 were smoothly deprotonated with lithium diisopropylamide and these lithiated species were reacted with 1 to give intermediates 8. The enol ether 2 (Z = OR) was obtained from 8 directly by heating at reflux or in two steps by quenching with water to give 9, followed by reaction of 9 with potassium tert-butoxide. For enolizable 1 high yields of 9 could be obtained by addition of 1 to lithiated 7 at -100 °C. Reagents 7a and 7b afforded THP enol ethers 2 (Z = OTHP), which were convertable to homologated aldehydes 3 with mild acid hydrolysis. Reagent 7c gave high yields of 1, 2-adducts 9, but these were not efficiently transformed to 2 (Z = OSi-t-BuMe2) by reaction with potassium tert-butoxide: the adduct from 7c and benzophenone gave 10 in 18% yield. © 1979, American Chemical Society. All rights reserved.