Homochiral group transfer in organic synthesis viaα-diazocarbonyl intermediates

Abstract

Optically active diazoketones derived from N-protected amino acids and (S)-2-chloropropionic acid have been used as homochiral group transfer reagents in the synthesis of various optically active a-functionalised ketones and related compounds.

Amination of Diazocarbonyl Compounds: N–H Insertion under Metal-Free Conditions

“…On the basis of previous reports − and our own observations, a plausible mechanism for the catalyst-free N–H insertion reaction between diazo compounds and dibenzenesulfonimide is proposed (Scheme ). Dibenzenesulfonimide 2a is known as a weak acid with p K a of 1.45, which may be partially ionized to generate a proton ion and a dibenzenesulfonimide anion (Scheme a).…”

“…Replacement of N -fluorobenzenesulfonimide (NFSI) with dibenzenesulfonimide resulted in a rapid formation of α-amino-ester derivative (Scheme c). Although the reaction of diazo compounds with acids, such as carboxylic acids, hydrogen halides and sulfonic acids are known in the literature, to our knowledge, insertion of D/A carbenoid precusors to imides has not been realized to date. Considering the ubiquitous motif of sulfonamides in pharmaceutical chemistry, we decided to explore this metal-free N–H insertion reactions systematically, and reported our preliminary results on this topic …”

Recent advances in stereoselective synthesis involving diazocarbonyl intermediates

“…(22)]. 47 Insertion into S-H bonds under rhodium(ii) catalysis provides access to a-sulfenyl ketones [eqn. (23)].…”

“…(23)]. 47 Aromatic cycloaddition, again with rhodium(ii) assistance, can be used to prepare cycloheptatrienes which rearomatise in the presence of trifluoroacetic acid to yield enantiopure a-amino benzyl ketones [eqn. (24)] from benzene.…”

Transition-Metal-Free Intermolecular α-Arylation of Ketones via Enolonium Species

“…Unfortunately, at the current stage of development such processes continue to rely on a directing group in the substrate that must be cleaved in a subsequent step. Sophisticated starting materials or potentially explosive diazo β-ketones are also prerequisites. , Baran reported an efficient super stoichiometric copper mediated radical anion reaction of in situ formed lithium-enolates with 2–3 equiv of unfunctionalized indoles and pyrroles in 30–67% yield (Figure c).…”