Carbenoids displacement reactions

A special method involves the carbenoid displacement reaction with diazocarbonyl compounds75, which is also used in an intramolecular fashion76. 

The carbenoid displacement reaction (see Section 1.4.5.2.1.4.) of the optically active acetoxy sulfide derivative 19 (or the corresponding methoxymethyl ether) with diazomalonate in the presence of a catalytic amount of rhodium acetate in refluxing benzene affords the tram-alkylation productl22. 

An intermolecular carbenoid reaction followed by intramolecular displacement of acetate gives the clavulanic acid derivative (112) in one step from 4-acetoxyazetidin-2-one (91) (80CC1257). Carbene-induced reactions of penicillins and cephalosporins have been reviewed (75S547, 78T1731). 

The procedures for the synthesis of cyclopropane derivatives, especially by the carbenoid route - " 49,55-57 Q, (ijg yjjjjg jQute (l.S-displacement), - have been amply reviewed. Equally well reviewed are the reactions of cyclopropanes and their use in synthetic methodologyFor the preparation of the more common cyclopropane derivatives, the use of suitably functionalized cyclopropyl building blocks that are commercially available would be recommended. 

Camphor oxa/olinc clni.il aiisili.nv 158 Caihanion intermediate in Giignaid reactions 235 Carbenoid intermediates 48 Caibocaiioiis 50 ( aibninaenesialioti 90 Carbon. nucleophilic displacement ai 27 -(>4 Caibonyl compound o 7. /n. 5... 

The mechanism of formation of benzvalene from cyclopentadienyl-lithium and dichloromethane has been studied in detail. On employing dideuteriodichloro-methane, the deuterium label is found to be stereospecifically located at the C-1 position of the product, in contrast to earlier reports. These data are compatible with two routes (i) chlorocyclopropanation of the cyclopentadienyl-lithium and subsequent nucleophilic displacement of the chloro-substituent and (ii) attack of the cyclopenta-dienyl anion on the dichloromethane to produce a cyclopentadienyl carbenoid A distinction between these two routes comes from a study of the reaction with indenyl-lithium. The exclusive formation of 1- and 2-deuterionapthalene (0.6 1) as byproducts is compatible only with the carbenoid path (Scheme 6) in which 1,2-cheletropic addition affords benzobenzvalene uniquely labelled at C-1, as is observed. 

The following section takes into account only reactions not involving transition elements. The nucleofiigal leaving group is generally a halide but may also be a sulfinate or an alkoxide. We have to differentiate between two distinct reaction modes, a two-step addition/elimination process on the one hand and a metal-assisted direct displacement of the nucleofuge from a carbenoid intermediate on the other. 

---