1 -Halo-1 -lithiocyclopropanes

In recent years, Seebach et al. have elaborated synthetic applications of ot-halo-lithiocyclopropanes, for instance, insertion of a CO-group between the two vinylic carbon atoms of an olefin (Eq. (43) 48)), annulations of four-membered rings and of lactones (Eq. (44) 9y), preparation of cyclopropylketones from olefins (Eq. (45) 49>), and, by using the same cyclopropylbromohydrins, bromovinylations S0) and synthesis of methyleneeyclopropanes from olefins, bromoform and aldehydes (Eq. (46)51)). 

Another feature of carbenoid-type reactivity is the cyclopropanation (reaction c). Again, this reaction does not only take place in vinylidene but also in alkyl carbenoids . On the other hand, the intramolecular shift of a /3-aryl, cyclopropyl or hydrogen substituent, known as the Fritsch-Buttenberg-Wiechell rearrangement, is a typical reaction of a-lithiated vinyl halides (reaction d) . A particular carbenoid-like reaction occurring in a-halo-a-lithiocyclopropanes is the formation of allenes and simultaneous liberation of the corresponding lithium halide (equation 3). ... 

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