The field of chiral catalysis has experienced explosive growth over the last two decades. By now, many of the classical reactions in organic synthesis can be carried out efficiently in asymmetric manner. As one of the fundamental and powerful C-C bond-forming reactions, enantioselective catalytic allylation (ECA) and crotylation (ECC) of aldehydes has attracted considerable attention. In this article, we present an overview about the importance of chiral Lewis acids and bases in catalytic enantioselective addition of allyl- and crotyl metals to aldehydes and the application of this methodology in the total synthesis of natural and non-natural products.

Compostos (E)-1,2-dibromo vinílicos 11a-f foram preparados estereosseletivamente via reação de bromação de alcinos empregando-se tribrometo de piridínio em MeOH/CCl4 a baixa temperatura e utilizados na reação de duplo acoplamento com PhZnCl catalisada por Pd(0), segundo protocolo de Negishi, fornecendo as respectivas olefinas tri e tetrassubstituídas 14a-e. Tamoxifeno, um agente antiestrogênico de uso clínico na terapia do câncer de mama, foi preparado na forma de uma mistura Z:E de proporção 2.3:1, em 7 etapas em um rendimento global de 30% a partir do 4-iodofenol (3).

(E)-1,2-vinylic dibromides 11a-f were stereoselectively prepared via bromination of acetylenic compounds with pyridinium tribromide in MeOH/CCl4 at low temperature and double cross-coupled with PhZnCl under Pd(0) catalysis (Negishi protocol) to afford tri- and tetrasubstituted olefins 14a-e. Tamoxifen, a selective estrogen receptor modulator clinically prescribed in breast cancer therapy, was prepared in 7 steps and 30% overall yield from 4-iodophenol (3) as a 2.3:1 mixture of (Z)- and (E)-isomers.