N-vinylation and N-allylation of 3,5-disubstituted pyrazoles by N-H insertion of vinylcarbenoids

Article abstract of DOI:10.1515/znb-2015-0115

A vinylcarbenoid approach toward N-functionalization of NH-pyrazoles is presented. The rhodium(II)- catalyzed reaction of methyl styryl-diazoacetate (1) or dimethyl 2-diazoglutaconate (3) with 3,5-disubstituted pyrazoles gave products of carbenoid N-H insertion in high combined yields, although regioselectivity issues posed by the pyrazole or the vinylcarbenoid moiety as well as positional and configurational isomerism concerning the C,C double bond of the latter led to product mixtures. The ambident reactivity of the vinylcarbenoid derived from 1 could be steered by the catalyst: While Rh₂(OAc)₄ yielded products of direct carbenoid insertion preferentially, silver(I) catalysis strongly favored reaction at the vinylogous site of the carbenoid resulting in an N-allylation of the pyrazoles.