Pyrrole‐Protected β‐Aminoalkylzinc Reagents for the Enantioselective Synthesis of Amino‐Derivatives

Abstract

Chiral β‐aminoalkylzinc halides were prepared starting from optically pure commercial β‐amino‐alcohols. These amino‐alcohols were converted to the corresponding N‐pyrrolyl‐protected alkyl iodides which undergo a zinc insertion in the presence of LiCl (THF, 25 °C, 10–90 min). Subsequent Negishi cross‐couplings or acylations with acid chlorides produced amino‐derivatives with retention of chirality. Diastereoselective CBS‐reductions of some prepared N‐pyrrolyl‐ketones provided 1,3‐subsituted N‐pyrrolyl‐alcohols with high diastereoselectivity. Additionally, a deprotection procedure involving an ozonolysis allowed the conversion of the pyrrole‐ring into a formamide without loss of optical purity.