5-methylene-1,3-cycloheptadiene

Zirconacyclopentadienes 23 (R = R = R = R = Et, Pr", Bu", M = Zr, Cp =Cp) react with l,4-dibromo-2-butyne in the presence of CuCl via a tandem inter-intra-molecular cyclization to yield 2,3,4,5-tetrasubstituted styrenes (Equation 11) <2002T1107>. 3-Chloro-(2-chloromethyl)propene reacts with the same set of zirconacyclopentadienes in the presence of CuCl to yield tetrasubstituted methylene cycloheptadienes. Reaction with 3,4-dichlorobutene under identical conditions yields vinylcyclohexadienes. In both cases, tandem inter-intra-molecular allylation occurs. 

The l-oxa-2,4,5-cycloheptatrienes 602 and 603 were postulated to be intermediates in the rearrangement of certain (ethynylfuryl)oxiranes to furo[3,4-b]furans [251]. The replacement of the methylene groups of 1,2-cycloheptadiene (465) by SiMe2 groups and the introduction of substituents at the allene moiety allowed the preparation of isolable seven-membered ring allenes. Thus, Barton et ah [177] obtained 604 and Ando et al. [178] 605. A few reactions of these systems have also been studied [177, 252]. Both groups [178, 253] synthesized the [4.4]betweenallene 606 and determined its structure by X-ray diffraction. 

Bicyclo 5.1.0 octan 8-Methylen-E19b, 526 (Ringverengung) 1,3-Cycloheptadien 5-Ethyl- V/lc, 659... 

Other approaches to chiral aziridines have been reported. For example, treatment of cycloheptadiene 725 with the leucine-derived (A)-3-acetoxyamino-2-(3-hydroxy-2,2-dimethylpropyl)quinazolin-4(3//)-one 724 in the presence of titanium(iv) /-butoxide (TTB) in methylene chloride leads to formation of the chiral aziridine 726, in which the chiral auxiliary (Q) is in the o-position, as the only isolated product in 29% yield (Scheme 175) <2001J(P1)1518>. 

The moderate conditions required for this conversion (E = 25.8 kcalmol" ) suggest that a planar diradical is not an appropriate intermediate ". The interconversions of several vinylmethylenecyclopropanes have been studied and [l,3]sigmatropic shifts can alone account for all the products, although some [3,3]shifts are not excluded For example, the syn and anti isomers of l-allylidene-2-vinylcyclopropane (211) undergo thermal isomerization into 4-vinyl-3-methylenecyclopentene (213) and 3-methylene-1,4-cycloheptadiene (214) on heating in cyclohexane at 42-ATC (equation 142). 

The stereocontroiied total synthesis of (+)-gelsemine was accomplished by T. Fukuyama and co-workers using the Knoevenagel condensation to prepare a precursor for the key divinylcyclopropane-cycloheptadiene rearrangement. The use of 4-iodooxindole as the active methylene component allowed the preparation of the (Z)-alkylidene indolinone product as a single stereoisomer. 

In addition to simple [3+2] cycloadditions described previously with methylene cyclopropanes, more complex variations using this same functionality provide efficient access to both seven- and nine-membered rings (Scheme 3-44). The fully intermolecular [3+2+2] cycloaddition of methylene cyclopropanes with two alkynes provides an efficient entry to cycloheptadiene derivatives. By moving to a partially intramolecular system, the efficient assembly of nine-membered ring products was illustrated by the [4+3+2] cycloaddition of methylene cyclopropanes with dienes tethered with an alkyne. ... 

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