Synthesis via haloketene cycloadducts
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1975
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The basic goal of this study was to develop new applications for haloketene cycloadducts in synthesis. This study has utilized the dichloroketene adduct of cyclohexene (5) as the starting material for the preparation of bicyclic diols 1 and 2. Another haloketene cycloadduct (31) was used as the starting material for the development of a novel approach towards the synthesis of sirenein (3) and sequicarene (4). Dicholorcyclobutanone 5 was readily converted to ketoacetate 12 by treatment with trimethylamine and acetic acid followed by chromous chloride reduction. Ketoacetate 12 could be converted to trans-diol 2 by treatment with lithium aluminum hydride. Cis-Diol 1 was formed by the aluminum iso-propoxide reduction of ketol 13. [Figures 5, 12, 2, 12, 13, 1] A rearrangement of chlorocyclobutanone 31 to ester 35 utilizing methanolic silver nitrate was the key step in forming the basic bicyclic structure of sirenin (3) and sesquicarene (4). Several methods for the introduction of the side chain were investigated. Desmethylsesquicarene (44) was prepared by one of these procedures. Methods for the introduction of the remaining methyl (or hydroxymethyl) group were investigated. [Figures 3, 4, 31, 35, 44]
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