Anosike IS, Beng TK. Harnessing the 1,3-azadiene-anhydride reaction for the regioselective and stereocontrolled synthesis of lactam-fused bromotetrahydropyrans by bromoetherification of lactam-tethered trisubstituted tertiary alkenols.
RSC Adv 2024;
14:18501-18507. [PMID:
38860240 PMCID:
PMC11163878 DOI:
10.1039/d4ra02523g]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Accepted: 06/05/2024] [Indexed: 06/12/2024] Open
Abstract
Halo-cycloetherification of lactam-tethered alkenols enables the construction of oxygen-heterocycles that are fused to nitrogen heterocycles via intramolecular halonium-induced nucleophilic addition. Specifically, tetrahydropyrans (THPs) that are fused to a nitrogen heterocycle constitute the core of several bioactive molecules, including tachykinin receptor antagonists and alpha-1 adrenergic antagonists. Although the literature is replete with successful examples of the halo-cycloetherification of simple mono- or disubstituted primary alkenols, methods for the modular, efficient, regioselective, and stereocontrolled intramolecular haloetherification of sterically encumbered trisubstituted tertiary alkenols are rare. Here, we describe a simple intramolecular bromoetherification strategy that meets these benchmarks and proceeds with exclusive 6-endo regioselectivity. The transformation employs mild and water-tolerant conditions, which bodes well for late-stage diversification. The hindered ethers contain four contiguous stereocenters as well as one halogen-bearing tetrasubstituted stereocenter.
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