Carbenoids with neighboring heteroatoms. III. Electrophilic reactions of two .alpha.-halocyclopropyllithium compounds

Abstract

Solutions of carbenoids 4a and 1 la were prepared by the reaction of alkyllithiums with dihalocyclopropanes 1. Carbenoid 4a had limited stability a t -80" but could be trapped by carbonation which gave 2 in low yield and by protonation which gave 4b in high yield. Bicyclobutane 5 was the major product of thermal decomposition of 4a. Carbenoid lla was more stable at -80" as evidenced by reactions with HtO, DnO, and benzophenone. Thermal decomposition of 1 la at -20' gave diene 14, presumably via dimerization of l-methoxycyclohepta-1,a-diene (16).

Stereoelectronic effects: Perlin effects in cyclohexane‐derived compounds

“…This compound was prepared in analogy to a published protocol. [ 19 ] A solution of dichlorospiroalkane 10 (200 mg, 1.30 mmol) in anhydrous Et 2 O (~3 ml) was added to lithium (18.7 mg, 2.68 mmol) dissolved at −78°C in liquid NH 3 (4 ml). The cooling bath was removed after 75 min and the mixture was slowly brought to rt.…”

“…A comparison of measured and calculated spectra suggested that the major isomer of dichloro compound 10 should bear the chlorinated carbon in pseudo‐axial orientation. However, reduction of 10 with lithium in liquid ammonia [ 19 ] led to the parent substrate 6 , whose isolation turned out to be quite tedious. Its volatility prevented an immediate isolation.…”

Lithium Carbenoids

“…Thus, the exo-bromine atom in dibromocyclopropane 25 is exchanged exclusively due to the methoxy substituent, which encourages the lithium to occupy the cis orientation (equation 16) 103 An alternative access to alkyl bromo lithio carbenoids is provided by the tin-lithium exchange reaction, as shown in equation 8 66,74 . When the carbenoid carbon atom is substituted by electron-withdrawing groups like carboxylic ester or keto groups, the carbenoid character is no longer maintained.…”

Carbenoids with neighboring heteroatoms. V. Nucleophilic reactions of lithium carbenoids of the exo-8-halo-3,5-dioxabicyclo[5.1.0]octyl system

“…Their comparison of intramolecular and intermolecular isotope effects allowed the c o n c h i o n s that either (1) no intermediate ( e g , a carbene or "carbene complex") intervened between the ahalolithium reagent and the y C -H insertion products, or (2) an intermediate was present, having been formed by way of a fully established preequilibrium. The reactions most extensively studied have been the cyclopropane-forming cy-~l o a d d i t i o n~.~ and the C-H insertion reactions,*v4 and with both reaction types, a-haloorganometallic compounds (carbenoids) have been implicated as reactive intermediates in a variety of cases.…”