Divergent Outcomes of Carbene Transfer Reactions from Dirhodium‐ and Copper‐Based Catalysts Separately or in Combination

Abstract

The use of copper and rhodium catalysts separately and in combination directs reactions between vinyldiazoacetates 3 and cinnamaldehydes 2 to from formal [4+3]-cycloaddition (epoxidation followed by Cope rearrangement), intramolecular cyclopropanation, and Mukaiyama-aldol reactions selectively and in high yield.

Hg(OTf)2 Catalyzed Intramolecular 1,4-Addition of Donor–Acceptor Cyclopropenes to Arenes

“…1 These efforts have prompted us to investigate reactions with diazo compounds of those transition metals having limited evidence for the formation of metal carbene intermediates. Mercury(II) is one such candidate having both a rich history as a π -acceptor electrophilic catalyst 2 and recent developments in metal-NHC chemistry, 3 but limited evidence for the intermediate formation of a reactive mercury-carbene intermediate.…”

“…4,5 The most relevant indicator for a mercury carbene in reactions of a diazo compound is that of mercury(II) catalyzed cyclo-propanation reactions of diazooxindoles which was reported in this journal by Zhou and co-workers. 5 We have recently described intramolecular C–H insertion reactions of N -benzyl-enoldiazoacetamides at the benzyl C–H bond to form β -lactams that occur in competition with the Buchner reaction at the aromatic ring of the benzyl group; 1a since these reactions occur in high yields with dirhodium(II), copper, and silver catalysts, we thought that C–H insertion/aromatic cyclo-addition of N -benzyl-enoldiazoacetamides could be a good indicator for the involvement of metal carbene intermediates. However, the use of highly electrophilic mercury(II) compounds with N -benzyl-enoldiazoacetamides has surprised us with its complexity and has led us to a novel Hg(OTf) 2 catalyzed intramolecular 1,4-addition reaction across the benzyl aromatic ring to form bicyclononatriene derivatives in high yield (Scheme 1).…”

“…1a However, the highly electrophilic mercuric triflate catalyzed dinitrogen loss with the formation of a product mixture dominated by the enol-silyl ether hydrolysis product 2a (Scheme 2). Enol-silyl ether hydrolysis products were also dominant in Hg(OTf) 2 catalyzed reactions with other enoldiazoacetamides and enoldiazoacetates.…”

“…Donor–acceptor cyclopropenes can be thermally generated from enoldiazoacetates and enoldiazoacetamides in quantitative yield 8 and are known to be capable of metal carbene formation in catalytic reactions. 1a,b,9 When cyclopropene 5a was used in place of 1a in the Hg(OTf) 2 -catalyzed reaction, the combined yield of the 1,4-addition product 4a and the Buchner reaction product 3a was improved to 58% (entry 1, Table 1). Since some hydrolysis of the initially formed silyl ether products was observed, trifluoroacetic acid was added to produce a more homogeneous mixture.…”

Cycloaddition reactions of enoldiazo compounds

“…Since the disclosure of tandem cyclopropanation/Cope rearrangement reactions, 135–153 the Davies group has been a major contributor to this area. Recently, they 154 and others 155 also developed [3+4]-methodologies that shared similar mechanistic pathways (vinylogous addition/ring closure) with the aforementioned [3+ n ]-cycloaddition reactions ( n = 1–3).…”