Catalytic enantioselective cross dehydrogenative coupling of sp3 C-H of heterocycles

C-C bond formation in heterocycles via the direct coupling of C-H bonds, under oxidative conditions, classified as cross dehydrogenative coupling (CDC), is without doubt one of the most atom efficient methods for the functionalization of these molecules. The most common is the coupling at the position alpha to the heteroatom, owing to the stabilization of forming carbocation by the heteroatom. The corresponding asymmetric versions, except for a few isolated reports, have been rather evasive for several years. Optically active heterocycles with the chiral center alpha to the heteroatom are widely present in natural products and pharmaceuticals, thus making them an attractive synthetic target. Persistent efforts towards the asymmetric CDC of heterocycles since the beginning of this decade have led to several developments in this challenging area. Particularly, in the last few years, considerable progress has been witnessed in this field. This review summarizes the progress made in the area of asymmetric cross dehydrogenative coupling of heterocycles in recent years. The review covers the catalytic asymmetric CDC of sp³ C-H bonds of the heterocycles with various coupling partners and illustrates the different catalytic systems employed.

Metal-free C(sp(3))-H functionalization: oxidative carbo-oxygenation of α-diazo carbonyls via radical dediazotization

A novel three-component carbo-oxygenation of α-diazo carbonyls for flexible synthesis of unprecedented α-aminooxy-β-amino ketones has been established through metal-free C(sp(3))-H functionalization from readily accessible N,N-dimethylanilines and N-hydroxyphthalimide. The reaction pathway involves an in situ-generated phthalimide N-oxyl radical-triggered dediazotization/radical coupling sequence, leading to C-O and C-C bond formation.

Cu(ii)-catalyzed cross-dehydrogenative coupling reaction of N′-acyl arylhydrazines and phosphites

A novel Cu(ii)-catalyzed cross-dehydrogenative coupling reaction of N′-aryl acylhydrazines and dialkyl phosphites has been developed for the synthesis of phosphorylhydrazides by using NMO as an external oxidant and AgNO₃ as additive.

Benzylation of heterocyclic N-oxides via direct oxidative cross-dehydrogenative coupling with toluene derivatives

A novel cross-dehydrogenative coupling (CDC) of heterocyclic N-oxides with toluene derivatives has been disclosed.

Efficient merging of copper and photoredox catalysis for the asymmetric cross-dehydrogenative-coupling of alkynes and tetrahydroisoquinolines

A highly efficient catalytic asymmetric alkynylation of prochiral CH2 groups in tetrahydroisoquinoline was developed using copper catalyzed cross-dehydrogenative-coupling of sp(3) and sp C-H bonds with the assistance of a photocatalyst and visible light.