Michael addition of malononitrile to chiral α-acylacrylates

Article abstract of DOI:10.1016/S0040-4020(01)87984-9

Starting from 2,3-O-isopropylidene-D-glyceraldehyde (1), 3-O-methyl and 3-O-benzyl-1,2-O-isopropylidene-α-D-xylo-pentodialdo-1,4-furanose (4a, 4b), we describe the synthesis of the α-acyl-β-alkyl substituted acrylates 2 and 5. The Michael addition of malononitrile to these substrates gives the polyfunctionalized 2-amino-4H-pyrans 3 and 6 with moderate diastereoselectivity and reasonable overall yield from diols 7 and 8a,b. A detailed analysis is performed scanning different type of bases in the Michael reaction. We find that, while for acceptor 2 no changes are observed, for compound 5 the stereochemical outcome of the 1,4-addition is reversed in going from piperidine, sodium hydride or potassium t-butoxide to lithium diisopropylamide or lithium diisopropylamide/magnesium iodide reagent. Several models fro rationalising the results are proposed.