Methylenecyclopropane ring-opening reaction

A related proximal ring-opening reaction is observed when trans- or cu-2,3-bis-(hydroxymethyl)methylenecyclopropanes react with Fe2(CO)9 in ether, affording a mixture of two noninterconvertible lactones (equation 341)403,404. It should, however, be noted... 

The double bond of methylenecyclopropanes is alkylated by carbonyl compounds in the presence of TiCLt [483]. While the bicyclic methylenecyclopropane in Eq. (199) suffered simple alkylation followed by chlorination to give the product as a single stereoisomer, monocyclic methylenecyclopropanes showed a quite different behavior, including a ring opening reaction to give alcohols with an allyl chloride moiety (Eq. 200). 

A short time after the first synthesis of a trimethylenemethane complex, Noyori et al. reported a new access to the class of compounds starting from methylenecyclopropane derivatives. While treatment of methylenecyclopropane with diironenneacarbonyl afforded 3 only in very poor yield in addition to (l,3-butadiene)tricarbonyliron, substituted systems such as 2-methyl-2-phenylmethylenecyclopropane (4) gave trimethylenemethane complexes such as 5 in up to 60% yield (Scheme 10.2) [14]. These results reflect the tendency of strained small rings to undergo ring-opening reactions in the presence of transition metal complexes. However, few stable complexes of methylenecyclopropane have been described [15]. 

Reaction of the cyclopropyl-substituted pivalate (25) with dimethyl benzylidenema-lonate in the presence of a palladium catalyst gave a mixture of alkylidenecyclo-propane (26) and vinylcyclopropane (27). The ratio of these two adducts is found to be quite sensitive to the choice of ligand and solvent. While triisopropyl phosphite favors the formation of the methylenecyclopropane (26), this selectivity is completely reversed with the use of the bidentate phosphite ligand dptp (12). Interestingly there was no evidence for any products that would have derived from the ring opening of the cyclopropyl-TMM intermediate (Scheme 2.8) [18]. 

Treatment of bicyclopropylidene (1) with lithium powder led to ring opening and subsequent treatment of the reaction mixture with dimethyl sulfate afforded the methylenecyclopropane derivative 225 and 4-octyne (226) in variable ratios (Scheme 51) [143]. 

Ruthenium complexes mediate the hydroamination of ethylene with pyridine.589 The reaction, however, is not catalytic, because of strong complexation of the amine to metal sites. Iridium complexes with chiral diphosphine ligands and a small amount of fluoride cocatalyst are effective in inducing asymmetric alkene hydroamination reaction of norbomene with aniline [the best enantiomeric excess (ee) values exceed 90%].590 Strained methylenecyclopropanes react with ring opening to yield isomeric allylic enamines 591... 

As with the chloropalladation reaction (vide supra)m the rearrangement of >/2-methyl-enecyclopropane to >/4-TMM was shown experimentally to proceed stereoselectively by disrotatory ring cleavage of the distal frontier molecular orbital considerations, which predict that the out-of-phase interaction between the metal orbital in the distal ring-opening of -methylenecyclopropane complexes can be minimized by bending the bond up away from the metal (equation 348)410 ... 

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