Acceptor-substituted vinylcyclopropanes

The reactions of vinyl ethers with vinyldiazoacetates unsubstituted at the vinyl terminus result in a very interesting outcome because either regioisomer of the [3 + 2] cycloadduct can be obtained (Scheme 14.16) [104]. An example is the reaction with 2,3-dihydrofuran where regioisomer 122 is formed via the established ring-opening reaction of the donor/acceptor-substituted vinylcyclopropane 121 under Lewis acidic conditions (Scheme 14.14) [104, 105]. The cyclopropanation step has been optimized to... 

Donor-acceptor-substituted vinylcyclopropanes such as (203) have been shown to undergo thermal ring enlargement to functionalized cyclopentene derivatives (204) at... 

Nucleophiles will open acceptor-substituted vinylcyclopropanes either by attacking the three-membered ring resulting in a 1,5-addition or by a 1,7-addition to the olefin moiety . In most cases two acceptor groups are a prerequisite for sufficient activation (see Chapter 9). An interesting nucleophile-dependent dichotomy is demonstrated by equation 143. Organoaluminium compounds add in a 1,5-fashion whereas the corresponding ate-complexes prefer the 1,7-mode . 

Buchert, M., Reissig, H. U. Rearrangement of donor-acceptor-substituted vinylcyclopropanes to functionalized cyclopentene derivatives. Evidence for zwitterionic intermediates. Liebigs Ann. Chem. 1996, 2007-2013. 

When donor-substituted and acceptor-substituted alkenes complex and suffer a one-electron transfer, the cation radical of the radical cation-radical anion pair may suffer rearrangement at rates competitive with back electron transfer or with radical ion pair recombination. Some vinylcyclopropanes show this phenomenon (127 —> 128 —> 129 —> 130) 2 TCNE and the diphenylbenzocyclobutene (131) react similarly to form (134) by way of (132) and (133).2 ... 

MO calculations have been carried out on the isomerization of cyclopropane to propene, and the MNDO method has been used to study the reaction pathway and to optimize the structure of reactant, transition structure, and product of the ring opening reaction of bicyclo[1.1.0]butane. Various methods have been employed to estimate the rate constants for ring opening of the 2-cyclopropyl-2-propyl radical. 1-Acceptor-1-sulfenyl-substituted 2-vinylcyclopropanes of the type (430) have been found to afford 6-sulfenyl-a,jS y, -unsaturated carboxylic esters and nitriles (431) upon treatment with acid, by a process which involves C(l)—C(2) bond fission and a novel 1,5-sulfenyl rearrangement (see Scheme 110). It has been shown that the benzophenone-sensitized photolysis of vinyl norcaradiene derivatives, such as 5-(2-methylprop-l-enyl)-3-oxatricyclo[4.4.0.0 ]deca-7,9-dien-4-ones (432), results in the regioselective cleavage of only one of the cyclopropyl c-bonds to afford isochroman-3-one derivatives (433). It has been reported that the major product obtained from the reaction of structurally diverse a-diazo ketones with an electron-rich alkene in the... 

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