An unusual stereoretentive 1,3-quaternary carbon shift resulting in an enantioselective Rh^II-catalyzed formal [4+1]-cycloaddition between diazo compounds and vinyl ketenes

Abstract

A Rh2(S-TCPTTL)4-catalyzed cyclopropanation of a vinyl ketene with a disubstituted diazo compound initiates a stereorententive, accelerated ring expansion to provide the cycloadduct in good to excellent yields and enantioselectivity.

A Phosphorus(III)‐Mediated (4+1)‐Cycloaddition of 1,2‐Dicarbonyls and Aza‐o‐Quinone Methides to Access 2,3‐Dihydroindoles

“…Based on our recent efforts in the C(3)‐functionalization of oxindoles employing diazooxindoles in a (4+1)‐cycloaddition, we sought to evaluate the comparative efficacy of a Rh(II)‐metallocarbene as the C 1 synthon with 2‐amino benzyl chlorides . Interestingly, treatment of aza‐ o ‐QM precursor 1a with diazooxindole 8 in the presence of Rh 2 (OAc) 4 and K 2 CO 3 yielded only recovered starting material.…”

(4+1)-Cycloadditions Exploiting the Biphilicity of Oxyphosphonium Enolates and RhII/PdII-Stabilized Metallocarbenes for the Construction of Five-Membered Frameworks

“…Inspired by reports by of Danheiser 39 and Rigby 40 the utilization of vinyl ketenes and vinyl isocyanates as four-atom synthons in conjunction with Rh IImetallocarbenes was reported by our laboratory as a viable retrosynthetic disconnect to afford formal (4+1)-cycliza-tions. 18,19,41 Through the cyclopropanation/vinyl cyclopropyl rearrangement of cyclopropyl vinyl ketenes/isocyanates via 1,3-carbon migration aided by the orthogonal cumulene -system we realized the synthesis of spirooxindole cyclopentenones and pyrrolones. 18,19,41…”

“…Additionally, 36 was isolated and characterized by X-ray crystallography and subsequently shown to convert into 30 under the optimized reaction conditions. 18,41 Scheme 14 Confirmation of cyclopropane 36 via a nucleophilic trapping experiment utilizing benzyl amine as the sequestering agent…”

Supramolecular Halogen Bonds in Asymmetric Catalysis

“…In a follow-up report, Charette et al demonstrated that (by omitting XB aceptor or donor fragments from the catalyst) at least three XBs must form among the ligands to obtain high levels of selectivity, leaving room for catalyst design ( Figure 13D; Lindsay and Charette, 2012). In the years since then, catalyst 45 or its analogs have been used in other enantioselective transformations, but catalytic applications have been the focus of the research (for selected examples, see: Goto et al, 2011;Liao et al, 2017;Rodriguez et al, 2018). As the shape of the catalyst and its effect on selectivity have been determined, the importance of the halogen bonding network has not been explored further and often is not mentioned in publications at all.…”