Efficient Catalytic, Oxidative Lactonization for the Synthesis of Benzodioxepinones Using Thiazolium-Derived Carbene Catalysts
摘要:
An efficient, oxidative carbene-catalyzed lactonization reaction has been developed. Using thiazolium precatalysts, a variety of benzodioxepinone products are accessible in good to excellent yields under mild and operationally simple conditions The reaction does not require high dilution conditions and proceeds via mild and selective oxidation with azobenzene, which can easily be recovered and reused applying inexpensive FeCl3 as a formal terminal oxidant
Various aromatic lactones have been synthesized and their regioselectivity (1,2-addition vs. 1,4- or 1,6-addition) investigated in reactions with organolithium species, particularly n-BuLi and sec-BuLi. The regioselectivity varied greatly depending on various factors, such as the bulkiness of both substrates and organolithium species, and types of solvent and cosolvent. In particular, 1,4-addition with dearomatization occurred preferentially using sec-BuLi as the nucleophile in tetrahydrofuran (THF) with hexamethylphosphoramide (HMPA) or N,N′-dimethylpropyleneurea (DMPU) as cosolvent. For sec-BuLi, the reaction was estimated to proceed through a single-electron transfer mechanism.
Efficient Catalytic, Oxidative Lactonization for the Synthesis of Benzodioxepinones Using Thiazolium-Derived Carbene Catalysts
作者:Christopher A. Rose、Kirsten Zeitler
DOI:10.1021/ol101854r
日期:2010.10.15
An efficient, oxidative carbene-catalyzed lactonization reaction has been developed. Using thiazolium precatalysts, a variety of benzodioxepinone products are accessible in good to excellent yields under mild and operationally simple conditions The reaction does not require high dilution conditions and proceeds via mild and selective oxidation with azobenzene, which can easily be recovered and reused applying inexpensive FeCl3 as a formal terminal oxidant