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Effects of alpha-Alkoxy Substitution and Conformational Constraints on 6-exo Radical Cyclizations of Hydrazones via Reversible Thiyl and Stannyl Additions.

ABSTRACT: 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(alpha)-C(=N) dihedral angle placing the C=N bond axial within a chairlike transition state, in contrast to the usual Beckwith-Houk model.

SUBMITTER: Friestad GK

PROVIDER: S-EPMC2034276 | biostudies-literature | 2007 Sep

REPOSITORIES: biostudies-literature

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Effects of alpha-Alkoxy Substitution and Conformational Constraints on 6-exo Radical Cyclizations of Hydrazones via Reversible Thiyl and Stannyl Additions.

Friestad Gregory K GK Mathies Alex K AK

Tetrahedron 20070901 38

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(alpha)- ...[more]

PMID: 18797497

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