Dirhodium Tetraacetate Catalyzed Carbon-Hydrogen Insertion Reaction in N-Substituted α-Carbomethoxy-α-diazoacetanilides and Structural Analogues. Substituent and Conformational Effects

Article abstract of DOI:10.1021/jo00042a018

A series of acyclic α-carbomethoxy-α-diazoacetanilides with different N-substituents, 5a-k, was prepared and the rhodium(II) acetate catalyzed reaction studied.It was found that the rhodium carbenoid reaction with these compounds occurred only at the N-substituent; when the N-substituent is a propargyl group, rhodium carbenoid addition to the triple bond is favored, resulting, ultimately, in the formation of a bicyclic furan derivative 8.With an N-(tert-butyloxycarbonyl)methyl substituent, interception of the rhodium carbenoid by the ester carbonyl oxygen occurred preferentially to give, eventually, 1,4-oxazine derivatives 9 and 9'.For N'-alkyl substituents, rhodium carbenoid carbon-hydrogen (C-H) insertion into the alkyl group to give the 2-azetidinone and/or 2-pyrrolidinone derivatives was observed.The chemoselectivity of the rhodium carbenoid C-H insertion can be altered by the use of the α-acetyl and α-phenylsulfonyl substituents.In these cases, exclusive C-H insertion at the N-aryl moiety resulted to give 2(3H)-indolinone products.However, the α-substituent effect on the chemoselectivity of the insertion reaction is easily overridden by conformational effects about the amide N-C(O) bond as revealed by the insertion reaction of the conformationally rigid compounds 20a-c.The α-substituent effects are reestablished when conformational rigidity is removed, as exemplified by the rhodium carbenoid insertion reactions of compounds 29a, b.