Synthesis of Enantioenriched Homopropargylic Alcohols through Diastereoselective SE' Additions of Chiral Allenylstannanes to Aldehydes

Article abstract of DOI:10.1021/jo00030a036

Allenylstannanes (S)-4 and (R)-4, available in ca. 90percent ee from alkynones 1 through reduction with the LiAlH4-Darvon alcohol or -ent-Darvon alcohol complex, followed by S_N2' displacement on the derived mesylates (R)-3 or (S)-3 with Bu3SnLi*CuBr*Me2S, readily add to various aldehydes under Lewis acid catalysis to afford optically active homopropargylic alcohols with good to excellent syn diastereoselectivity.With 2-(benzyloxy)propanal (48), MgBr2-catalyzed reactions are highly stereoselective, affording the syn adduct 49 from the (S)-stannane (S)-4 and the anti adduct 52 from the (R)-stannane (R)-4.BF3-promoted additions give mainly or exclusively the syn adducts 49 and 51.Additions of (S)- and (R)-4 to (R)-3-(benzyloxy)-2-methylpropanal (61) yield the syn adducts 62 and 64 as major or exclusive products.