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Abstract: Catalytic asymmetric syntheses of (−)-centrolobine and (−)-de-O-methylcentrolobine have been achieved, incorporating a hetero-Diels–Alder (HDA) reaction between 4-aryl-2-silyloxy-1,3-butadienes and phenylpropargyl aldehyde derivatives as a key step. The HDA reaction using dirhodium(II) tetrakis[(R)-3-(benzene-fused-phthalimido)-2-piperidinonate], Rh2(R-BPTPI)4, as a chiral Lewis acid catalyst provides exclusively cis-2,6-disubstituted tetrahydropyran-4-ones in up to 93% ee. [Copyright &y& Elsevier]

The first example of a chiral Lewis acid-catalyzed enantioselective hetero-Diels–Alder (HDA) reaction between 1-dimethylamino-3-silyloxy-1,3-butadiene (Rawal’s diene) and aldehydes is described. The cycloaddition reaction under the influence of 1 mol% of dirhodium(ii) tetrakis[N-benzene-fused-phthaloyl-(S)-piperidinonate], Rh2(S-BPTPI)4, proceeded cleanly and gave, after treatment with acetyl chloride, the corresponding dihydropyranones in up to 99% ee. [ABSTRACT FROM AUTHOR]