Cyclopropyl ring, cleavage

Cleavage of cyclopropyl rings in the presence of an acid or base is illustrated by tlie tritiation of the 19-angular methyl group in 5, 19-cycloandrostane-3, 17-dione [(239) (240) R = T]. This reaction is carried out by heating... 

Earlier in this section we represented -cleavage as an opening of the cyclopropyl ring to yield a biradical. However, an alternative possibility exists/681 For example, of the intermediates in the following,... 

Reaction of bis(pinacolato)diboron to methylenecyclopropanes proceeds with cleavage of the proximal G-C bond of the cyclopropyl ring, giving 2,4-diboryl-l-alkenes (Equation (14)).74... 

The cleavage of the cyclopropyl ring with its relase of the total strain is a powerful driving force. Electrophilic attack on the electron rich ring does provide one approach as shown in Eq. 13). The lack of selectivity in the cleavage of one of the... 

On the other hand, if the non-classical ion is a stable intermediate, the transition state for the 3,2 hydride shift requires a subst mtial reorganization, including the cleavage of the cyclopropyl ring, and, by analogy with unimolecular gas phase processes, a much higher pre-exponential factor might be expected. [In the cyclopropane-propylene reaction log A is 1ST 7 (Chambers and Kistiakowsky, 1954).] Contrary to expectation, the observed pre-exponential for the 3,2-shift is actually a little lower than for the 1,2,6-equilibration process. 

Cyclization of substrates containing a cyclopropyl substituent proceeds with concomitant cleavage of the cyclopropyl ring. 

The regioselectivity in ketyl-radical-promoted ring cleavage of configurationally restricted tricyclo[3.3.0.0 ]octanone derivatives was investigated by Maiti and Lahiri, revealing new and additional information for this class of compounds in contrast to simple and unrestrained cyclopropyl ketones [9],... 

The addition of lithium to dicyclopropylacetylene (556) catalyzed by biphenyl (3%) in THF at —30 °C provoked a carbon-carbon bond cleavage in one of the cyclopropyl rings giving a delocalized dianion 557, which by reaction with dimethyl sulfate at —78 °C gave the aUtene 558 (Scheme 149). ... 

The isomerizatioA of 84S contrasts in a striking way with the response of bis-cyclopropyl ether 848 to electrophilic ring cleavage. In acidic methanol, cleavage of the cyclopropane ring toward oxygen results to give 849... 

On the other hand, a recent crystallographic study revealed that the trans-2-phenylcyclopropylamine (8a) forms a cyclopropyl ring-opened adduct with MAO B at the flavin C(4a), and no evidence was obtained for inhibitor binding at Cys-365 [70,127]. From this observation, Edmondson and coworkers suggested [70] that the inhibition mechanism might be accommodated by a mechanism similar to that proposed by Sayre et al. for the quinone-mediated oxidative cleavage of cyclopropylamines [128]. 

The proposed mechanism of the ring cleavage reaction of HCI (and other protic acids) with cyclopropyl carbynyl complexes involves addition of HQ across the carbyne triple bond to give a carbene complex as key intermediate. In the absence of a carbonyl ligand this is followed by ring expansion to a metallacyclopentene complex, /J-hydrogen elimination and reductive elimination to the diene complex (equation 111)164. 

Reduction of the ester group to give secondary alcohol 54 and sub sequent protection with /e/t-butyldimethylsilyl chloride leads to si-lyl ether 55 Oxidative cleavage of the cyclopropyl ring in this system proceeds through a radical mechanism and results in ben/oate ester 56. Basic ester hydrolysis gives piimar> alcohol 16... 

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