Double Conjugate Addition of Dithiols to Propargylic Carbonyl Systems To Generate Protected 1,3-Dicarbonyl Compounds

The work describes the efficient double conjugate addition of ethane and propane dithiols in the presence
of sodium methoxide to a wide variety of propargylic carbonyl containing compounds. The products of
these reactions are differentiated, 1,3-dicarbonyl systems useful for various synthesis programs. By
judicious use of hydroxylated substrates tandem cyclization occurs to afford tetrahydropyran lactols or,
in the case of hydroxy-substituted propargylic esters, lactones. The corresponding amino-substituted
propargylic aldehydes gives piperidine derivatives upon double conjugate addition tandem cyclization.