Koh and co-workers disclosed a nickel-catalyzed three-component
synthesis of acyl C-glycoside, wherein they realized the consecutive
cross-electrophile couplings of three different organohalide substrates,
namely, glycosyl halides (195 ), organoiodides (197 ),
and isobutyl chloroformate (196 ) (Scheme 27).[35] The reaction features a wide scope of various
functionalized organoiodides and glycosyl halides, producing desired
products in good yields (Scheme 27-B). Notably, high 1,2-trans
selectivity was observed in coupling partners derived from furanose
(198a–198n ), D-mannopyranose (198o–198q ), and
L-rhamnopyranose (198v–198x ). Glycosyl halide coupling
partners derived from D-glucopyranose (198r ), D-galactopyranose
(198s, 198t ) and L-fucopyranose (198u ) produced good
1,2-cis selectivities. The synthetic applicability of the developed
methods was further underlined by the glycosylation of oligopeptides
(198y–198ae , Scheme 27-C) and the preparation of (1→2)-linked
C-disaccharides (198ag–198aj , Scheme 27-D).
Preliminary mechanistic studies provide evidence supporting that the
oxidation of the active ligated Ni(0) species by isobutyl chloroformate
occurs preferentially, and cross-electrophile coupling between isobutyl
chloroformate with organoiodides likely precedes the subsequent coupling
with glycosyl chloride. Based on
Scheme 27 Nickel-catalyzed multicomponent synthesis of acyl
C-glycosides