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Tin-Free Access to the ABC Core of the Calyciphylline A Alkaloids and Unexpected Formation of a D-Ring-Contracted Tetracyclic Core.

ABSTRACT: A tin-free strategy for the successful cyclization of a variety of internal alkyne-containing N-chloroamine precursors to the ABC core via cyclization of a neutral aminyl radical is established. Deuterium labeling experiments confirm that the solvent is the primary source of the final H atom in the cyclization cascade. These conditions enabled a streamlined route to a β-ketoester intermediate poised for intramolecular Knoevenagel condensation to construct the seven-membered D-ring of calyciphylline A alkaloids. However, exposure to CsF in t-BuOH at elevated temperatures led to an unexpected decarboxylation to form a D-ring-contracted tetracyclic core.

SUBMITTER: Lopez AM

PROVIDER: S-EPMC6221184 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

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Tin-Free Access to the ABC Core of the Calyciphylline A Alkaloids and Unexpected Formation of a D-Ring-Contracted Tetracyclic Core.

Lopez Alberto M AM Ibrahim Ahmad A AA Rosenhauer Gregory J GJ Sirinimal Hansamali S HS Stockdill Jennifer L JL

Organic letters 20180403 8

A tin-free strategy for the successful cyclization of a variety of internal alkyne-containing N-chloroamine precursors to the ABC core via cyclization of a neutral aminyl radical is established. Deuterium labeling experiments confirm that the solvent is the primary source of the final H atom in the cyclization cascade. These conditions enabled a streamlined route to a β-ketoester intermediate poised for intramolecular Knoevenagel condensation to construct the seven-membered D-ring of calyciphyll ...[more]

PMID: 29613805

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