Carbenoid Reactions in Rhodium(II)‐Catalyzed Decomposition of Iodonium Ylides

Abstract

The intermediacy of metallocarbenes in decomposition reactions of iodonium ylides with [Rh,(OAc),] was established by comparison with reactions of the corresponding diazo compounds. The sensitivity of the Rh"-catalyzed intermolecular cyclopropane formation from substituted styrenes and bis(methoxycarbonyl)(phenyliodono)methanide (la) or dimethyl diazomalonate (lb) is identical. The Hummerr plot (with a ' ) has a slope of -0.47. Iodonium ylides and diazo compounds afford the same products in [Rh,(OAc),]-catalyzed cyclopropane formations, cycloadditions, and intramolecular CH insertions, and exhibit the identical selectivity in intramolecular competitions for cyclopropane formation and insertion. The intramolecular CH insertion of the ylide ZOe, when carried out in the presence of a chiral catalyst ([Rh2{(-)-(S)-ptpa}4]), results in formation of 21a having an ee of 67%, identical to the ee obtained with the diazo compound 20b.Introduction. -The decomposition of diazoketones and diazoesters in the presence of chiral transition-metal catalysts has a remarkable potential for asymmetric catalysis [I]. Cu-Based catalysts [2-51 found successful applications in intermolecular cyclopropane formation with olefins, while chiral Rh"-complexes provided products of intramolecular cyclopropane formation [6], CH insertion [7-91, and intermolecular cyclopropene formation of acetylenes [lo] having enantiomeric excesses in the range of 95% or more. The major drawback of these reactions is the requirement of diazo compounds as precursors which are potentially explosive, toxic, or/and carcinogenic [ 1 11.The transition-metal-catalyzed decomposition of diazo compounds leads to metallocarbenes which are not isolable, but transfer the carbene moiety to a suitable acceptor molecule or to an appropriate reactive site within the metallocarbene [l]. Thus, the use of diazo compounds might be avoided if it were possible to generate the metallocarbenes from other precursors. This investigation deals with the use of iodonium ylides [12-151 as precursors for metallocarbenes in view of their application to asymmetric catalysis.The photochemical and transition-metal-catalyzed decomposition of iodonium ylides such as l a (bis(methoxycarbonyl)(phenyliodono)methanide) [

Diazo‐ and Transition‐Metal‐Free CH Insertion: A Direct Synthesis of β‐Lactams

“…As shown, the insertion product 17 c was preferentially formed (Scheme ). Interestingly, this selectivity in favor of CH insertion is in contrast to prior reports employing Rh II catalysis 18c…”

One-pot synthesis and chiral analysis of cyclopropane derivatives

“…1) are usually assumed to be involved in the metal-catalyzed cyclopropanation reactions with phenyliodonium ylide. 9 The use of ylides as cyclopropanation reagents dates back to the work done by Corey et al 10 and developed since then by many groups. 11 However, the reported processes involve the synthesis of the ylide in a separate step.…”

Continuous Processing and Efficientin SituReaction Monitoring of a Hypervalent Iodine(III) Mediated Cyclopropanation Using Benchtop NMR Spectroscopy

“…A multiple monitoring technique approach, using compact mass spectrometry with benchtop NMR (CMS-NMR), was developed in order to provide complementary analytical information for the cyclopropanation of phenyl iodonium ylide. Phenyl iodonium ylide derivatives are widely used in carbene-transfer reactions including cyclopropanation, presenting a comparable reactivity to their diazo counterparts under milder conditions . The iodonium ylide method takes advantage of the readily generated carbene species, induced by metal catalysis, displacing the molecular iodobenzene which then cyclizes in the presence of an olefin.…”