Broad-Scope Rh-Catalyzed Inverse-Sonogashira Reaction Directed by Weakly Coordinating Groups

Abstract

We report the alkynylation of C(sp2)–H bonds with bromoalkynes (inverse-Sonogashira reaction) directed by synthetically useful ester, ketone, and ether groups under rhodium catalysis. Other less common directing groups such as amine, thioether, sulfoxide, sulfone, phenol ester, and carbamate are also suitable directing groups. Mechanistic studies indicate that the reaction proceeds by a turnover-limiting C–H activation step via an electrophilic-type substitution.

Cobaltaelectro‐Catalyzed C—H Acyloxylation

“…To this end, an intermolecular competition experiment revealed electron-donating carboxylic acids to be inherently more reactive (Scheme 4a). This observation is in good agreement with a base-assisted internal electrophilic-type substitution (BIES) [13] mechanism for the key C-H scission. Moreover, cobaltaelectrocatalysis in the presence of isotopically labeled CD 3 OD did not lead to H/D scrambling, while illustrating the C-H functionalization to be fully tolerant of protic solvents (Scheme 4b).…”

Rhodium(III)‐Catalyzed C−H Alkynylation of N‐Methylsulfoximines

“…On the basis of previous reports, a plausible mechanism was proposed as below (Scheme ). The catalytic cycle is initiated by coordination of Rh III species to sulfoximines and subsequent C−H activation with assistance of ligated base generates a five‐membered rhodacycle intermediate I .…”

“…On the basis of previous reports, [11] ap lausible mechanism was proposed as below (Scheme4). The catalytic cycle is initiated by coordination of Rh III species to sulfoximinesa nd subsequent CÀHa ctivation with assistance of ligated base generates af ive-membered rhodacycle intermediate I.T he intermediate undergoes ligand exchange to coordinate with bromoacetylene 2,f ollowed by alkyne insertiona nd Ag 2 CO 3 -assisted bromide elimination delivers the final products 3 and regenerates rhodium(III) catalyst.…”

Fundamental and Applied Aspects of the Chemistry of Acetylenylquinones

“…The deacetylation of 2 via MeONa in MeOH produced the mono-C-glycoside 4 in a yield of 96 %, whereas the corresponding bis-C-cellobiosyl derivative 6 was obtained in a 70 % yield through treatment with 5 in the presence of KCN in MeOH/CH 2 Cl 2 followed by column chromatography. In addition to the traditional technique employed for the synthesis of acetylenylanthraquinone analogs, Tan et al proposed a fundamentally different way of alkynylating 9,10-anthraquinone via the substitution of a hydride [11]. Here, substrates that possessed electron-accepting substituents, such as carbonyls, esters, and other similar groups, could be used for the alkynylation of C(sp 2 )-H bonds with bromalkines under Rh-catalyzed cross-coupling (pseudo-Sonogashira) reactions ( Figure 5).…”