Cyclopropanes oxidative rearrangement

The mode of formation of formaldehyde is of interest in the case of cyclopropane oxidation. The mechanism advanced involved a complex rearrangement of the cyclo-propylperoxy radical to formaldehyde and CH3CO. The degenerate-branching reaction of formaldehyde was formulated on the following considerations. Lead oxide which markedly inhibits the oxidation of methane (26), presumably by efficient heterogeneous destruction of H02 radicals, is known to exert a similar effect on cyclopropane combustion... 

Due to efforts of Conia s (equation 148) and Trost s groups access to more substituted vinylcyclopropanes has been gained operating with siloxy derivatives prepared either by Simmons-Smith cyclopropanation or using diphenylsulphonium cyclopropylide as a key substance (see Section VI.D.l). Oxidative rearrangement has led to a cyclopentanol... 

Treatment of bicyclo[4.1.0]heptan-2-ols with perchloric acid in acetic acid caused very clean rearrangement with formation of cyclohept-3-enyl acetates (Table 1). Only in the case of cxo-7-methylbicyclo[4.1.0]heptan-2-ol was the cyclohex-2-enyl acetate the major product probably because the 7-methyl group conferred additional stabilization on the carbocation formed by j0-scission of the outer cyclopropane bond. The same type of reactant could be oxidatively rearranged using pyridinium chlorochromate to afford cyclohepten-4-ones, together with (chloromethyl)cyclohexenes. However, if the chloride in the reagent was replaced with tetrafluoroborate, or if pyridinium chlorochromate was used with silver(I) nitrate, formation of the substituted cyclohexenes was completely suppressed, e.g. formation of 7 from 6, although the reported yields were low. ... 

TroponesReaction of vinyldiazomcthanes (1) with l-methoxy-l-(trimethyl-silyloxy)butadiene (2) catalyzed by rhodium(H) acetate or rhodium(ll) pivalate results in [3+4]cycloaddition via cyclopropanation/Cope rearrangement to form a cyclohcptadiene (3). Short exposure of 3 to citric acid followed by oxidation (DDQ) provides the... 

The key step in this sequence, achieved by exposure of 46 lo a mixture of sulfuric acid and acetic anhydride, involves opening of the cyclopropane ring by migration of a sigma bond from the quaternary center to one terminus of the former cyclo-l>ropane. This complex rearrangement, rather reminiscent of the i enone-phenol reaction, serves to both build the proper carbon. keleton and to provide ring C in the proper oxidation state. 

The synthesis of compounds 39, 41, and 43 by the ODPM rearrangement opens a novel photochemical route to chrysanthemic acid and other cyclopropane carboxylic acids present in pyrethrins and pyrethroids [52]. In fact, aldehyde 43 can be transformed to tran -chrysanthemic acid by simple oxidation. This new synthetic route to ecologically benign insecticides competes with the one previously described by us using the 1-ADPM rearrangement of p,y-unsaturated oxime acetates [30,53]. 

In the past few years, new approaches for the enantioselective synthesis of / -benzyl-y-butyrolactones appeared in the literature. Some of these approaches involve the asymmetric hydrogenation of 2-benzyl-2-butenediols (j [34]), the radical mediated rearrangement of chiral cyclopropanes (r [35]), the transition metal catalyzed asymmetric Bayer-Villiger oxidation of cyclobutanones n [36]), or the enzymatic resolution of racemic succinates (g [37]). 

Dipolar cycloadditions of nitrile oxides 216 onto 1 gave much poorer yields of cycloadducts 217 than those of nitrones 205. The cycloadditions of 216 to 1 require higher temperatures and unfavorably compete with their dimerization to furoxanes. However, stable nitrile oxides 216 with bulky substituents R that hamper dimerization, can be used. The thermal rearrangements of 5-spirocyclopropane-annelated isoxazolines 217 always required higher temperatures than the isoxazolidine counterparts. Under these conditions the second cyclopropane ring was also cleaved to give furopyridines 218 (Scheme 48) [136, 137]. 

Hydroxymelhyl)cyc opropan-l-ol (11), readily obtained by hydrogen peroxide oxidation of methylenecyclopropane, was rearranged to cyclobutanone (12) either directly, or via an intermediate l-(tosyloxymethyl)cyclopropan-l-ol.114 115 Competitive ring opening to 1-hydroxy-butan-2-one (13) was observed in the boron trifluoridc catalyzed process. 

Bicyclo[3.2.0]heptan-6-ones 10 were obtained by transformation of 2-methoxycyclohex-2-enones 8 to l-methoxybicyclo[4.1.0]heptan-2-ols 9 and subsequent rearrangement (Table 13).155 161 For the synthesis of the requisite precursors, a sequence of reduction and cyclopropanation 8 - 9, eventually followed by oxidation and an addition to the carbonyl group 9 — 11 — 12, proved most effective. 

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