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[reaction: see text] Asymmetric dihydroxylation, thiyl radical mediated transfer of a silicon-tethered vinyl group to a hydrazone and an unconventional aldehyde-selective Wacker oxidation are sequenced for an efficient synthesis of methyl N-trifluoroacetyl-L-daunosaminide in 32% overall yield from crotonaldehyde.

Access to multifunctional hydrazones of relevance to dysiherbaine synthesis studies is described. Subsequent radical cyclizations of multifunctional hydrazones via a Si-and C-linked tethering strategy are shown to function effectively in 6-exo fashion. Conformational constraints are proposed to play a key role in suppressing unproductive premature reduction pathways. The stereochemical outcomes suggest that minimizing the dipole repulsion between neighboring C=N and C-O bonds favors a C α -C(=N) dihedral angle placing the C=N bond axial within a chairlike transition state, in contrast to the usual Beckwith-Houk model.

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No abstract