Catalytic, Asymmetric Vinylogous Mukaiyama Aldol Reactions of Pyrrole- and Furan-Based Dienoxy Silanes: How the Diene Heteroatom Impacts Stereocontrol

✍ Scribed by Claudio Curti; Beatrice Ranieri; Lucia Battistini; Gloria Rassu; Vincenzo Zambrano; Giorgio Pelosi; Giovanni Casiraghi; Franca Zanardi

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 308 KB
• Volume: 352
• Category: Article
• ISSN: 1615-4150
• DOI: 10.1002/adsc.201000189

✦ Synopsis

Abstract

Denmark’s chiral bisphosphoramide/silicon tetrachloride system performs as an excellent Lewis base‐Lewis acid catalyst for the vinylogous Mukaiyama aldol reaction of pyrrole‐ and furan‐based dienoxy silanes with aromatic and heteroaromatic aldehydes. This asymmetric methodology provides a powerful synthetic entry to a variety of δ‐hydroxylated γ‐butenolide‐type frameworks with high efficiency and valuable margins of regio‐, diastereo‐, and enantioselectivity. Notably, the nature of the heteroatom within the vinylogous dienoxy silane donor heavily impacts the diastereocontrol, with syn‐configured aldol adducts emerging from pyrroles bearing electron‐withdrawing N‐protecting groups (Boc, Ts, and Cbz) and anti‐configured adducts prevailing when furan‐ or N‐alkyl/alkenylpyrrole donors are involved.