The Homoaldol Reaction, or How to Overcome Problems of Regio‐ and Stereo‐selectivity

Abstract

Abstract Even today, there are conspicuous gaps in the register of organic synthetic methods. Thus, numerous types of homoenolate reagents are listed; yet no generally applicable method for the homologue of the aldol addition, viz. the homoaldol addition, is to be found. The methods documented up to 1980 offer only singular solutions, and, moreover, are not stereoselective. The present article gives an overview of the existing possibilities and then describes how the gap can be closed by using a new class of homoenolate reagents: 2‐alkenyl esters of N,N ‐diisopropylcarbamic acid are lithiated and the resulting allyllithium compounds tailored to high regio‐ and diastereoselectivity in addition reactions to the carbonyl group via metal exchange. Altogether, the homoaldol reactions now offer a general and reliable, highly stereoselective entry to γ‐hydroxycarbonyl compounds, whereby the C(β)C(γ) bond is formed. Furthermore, it is demonstrated how problems associated with the application of allyl anions as synthetic reagents can be solved today.