Ashtekar KD, Gholami H, Moemeni M, Chakraborty A, Kiiskila L, Ding X, Toma E, Rahn C, Borhan B. A Mechanistically Inspired Halenium Ion Initiated Spiroketalization: Entry to Mono- and Dibromospiroketals.
Angew Chem Int Ed Engl 2022;
61:e202115173. [PMID:
34881491 PMCID:
PMC9254888 DOI:
10.1002/anie.202115173]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Indexed: 11/09/2022]
Abstract
Employing halenium affinity (HalA) as a guiding tool, the weak nucleophilic character of alkyl ketones was modulated by the templating effect of a tethered 2-tetrahydropyranyl(THP)-protected alcohol towards realizing a bromenium ion initiated spiroketalization cascade. Addition of ethanol aided an early termination of the cascade by scavenging the THP group after the halofunctionalization stage, furnishing monobromospiroketals. Alternatively, exclusion of ethanol from the reaction mixture biased the transient oxocarbenium towards α-deprotonation that precedes a second bromofunctionalization event thus, furnishing dibrominated spiroketals. The regio- and stereoselectivity exploited in the current methodology provides a novel and rapid access to the dibrominated spiroketal motifs exhibited by several natural products.
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