Bicyclo pentane, insertion

Dicyano-substituted triafulvenes react with enamines to produce exclusively the cross-conjugated dicyanomethylene compounds 519, whose formation can be rationalized by a methylene bicyclo(2,l,0)pentane intermediate 51879 296 Since cyclanone enamines 520 and other cyclic enamines 522 react analogously, this C-C-insertion 237) of the triafulvene ring skeleton into the enamine C=C bond represents a versatile ring expansion mode (C + C3), which makes accessible a series of unsaturated medium-ring compounds (521/523) that are otherwise difficult to synthesize. 

Carben.es insert into a C — H bond of a cyclobutane.157 When there is a choice between a cyclopropane and a cyclobutane C — H bond, as in bicyclo[2.1. OJpentane, the insertion of phenylcarbe-ne takes place at a cyclobutane methylene position to give 2-benzylbicyclo[2.1.0]pentane (l).157... 

The known synthetic approaches to [1.1.1 ]propellanes can be divided into three general categories (Scheme 1) (i) intramolecular carbene insertion in a 3-methylenecyclobut-l-ylidene, (ii) intramolecular anionic ring closure in a bridgehead-substituted bicyclo-[1.1.0]butane, and (iii) 1,3-elimination in a bicyclo[l.l.l]pentane. 

Addition across carbon—halogen bonds. Alkyl iodides48,62,65,109 "3,114 and also activated bromides48,65,107 "3,115 (e.g. methyl bromoacetate) react with la thermally62 or under UV irradiation to give 1,3-disubstituted bicyclo[l. 1. l]pentanes when the reaction is performed in diethyl ether, and the insertion of a single bicyclo[l. 1. l]pentane cage can be viewed as the standard reaction pattern. 

Three phosphonites (RO)2PR have also been found to add to la. The products contained the bicyclo[l.l.l]pentane cage inserted into the P—C bond and were isolated after oxidation to stable pentavalent phosphorus derivatives125. In a related process involving... 

Electrophilic addition reactions of carbenes to cyclopropane structures are rare and not synthetically important. Reaction of carbenes with bicyclo[2.1.0]pentane generally gave products arising from C —H insertion at one of the methylene groups of the four-membered ring. ° An exception was difiuorocarbene which gave 1,1-difluorohexa-l,5-diene (2) in very low yield by cleavage of two C —C bonds. - ... 

In general, photolytic azo-extrusion from 4,5-dihydro-3/f-pyrazoles is superior to thermolysis. Photolysis was introduced as a method for synthesis by Jeger s group (Kocsis et al., 1960). The configurations of the products in the thermolysis, in the direct photolysis, and in the sensitized photolysis are often quite different. Cyclopropanation for the synthesis of alkyl cyclopropanes via dihydropyrazoles is preferred to the direct route via carbenes, because, in the latter, the C - H insertion of the carbene into the alkyl group is faster than the cyclopropanation. The dihydro-pyrazole pathway was used in particular for the formation of highly strained bicyclo[1.1.0]butanes (Franck-Neumann, 1967 Komendantov and Bekmukhametov, 1971 6.89) and bicyclo[2.1.0]pentanes (Vogelbacher et al., 1984 6.90). 

The Ni° catalysed rearrangement of bicyclo[2.1.0]pentane (60, cf. Table 8 entry lb) leads to metal insertion into the central C—C bond of the bicyclopentane in the primary step (equation 25). Successively, the trapping alkene ZCH=CHZ attacks a Ni—C... 

Transition-metal-catalysed rearrangements of bicyclo[2,l,0]pentanes have been examined with the aid of deuterium labelling and the evidence so far is consistent with an insertion of the metal into the internal bond of the bicycloalkane to give a metallo-cyclic intermediate. On the other hand, the reaction of the alcohol (774 n = 1—3) with a palladium salt gives the product (775) of opening of an external bond of the cyclobutane ring. ... 

The cleavage of the three-membered ring in bicyclo[2,l,0]pentanes and spiro-[4,2]heptadienes can be effected by metal carbonyls, and with the latter organic substrates carbonyl insertion reactions are observed. 

The stereochemical consequences of the previously reported vinylogous WolfP rearrangement involved in the copper-catalysed decomposition of Py-unsaturated diazoketones, for example (52a, b, and c) prepared from the esters (53a, b, and c), have been explored. The reaction pathway could reasonably lead through a bicyclo[2,l,0]pentane intermediate, via insertion of the diazocarbon into the Py-olefin, which could then fragment, possibly in a stepwise manner. Whereas (52a) and... 

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