Stereoselective Synthesis of syn-β-Amino Propargylic Ethers: Application to the Asymmetric Syntheses of (+)-β-Conhydrine and (-)-Balanol

The stereoselective synthesis of syn-beta-amino propargylic ethers by the addition of racemic lithio 3-(methoxymethoxy)allenylcuprates, and more particularly (cyano) and (mesityl)cuprates, to enantiopure chiral N-tert-butylsulfinylimines is reported. The scope and limitations of the reaction is studied. The usefulness of the methodology for the synthesis of compounds having a syn-1,2-amino alcohol unit is shown through the development of the asymmetric syntheses of (+)-beta-conhydrine and of an advanced intermediate of (-)-balanol.