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-other | 2018 Apr

REPOSITORIES: biostudies-other