Cyclopropanols rearrangement

Vinyl cyclopropanols have been prepared by the addition of alkenyl Grignard reagents to a variety of cyclopropanone equivalents. Upon treatment with acid, the vinyl cyclopropanols rearrange to a-substituted cyclobutanones. Alternatively, a variety of a-heteroatora-substituted cyclopropyllithiura reagents have been developed. These react with aldehydes and ketones to afford cyclopropylcarbinols which also rearrange to cyclobutanones under acid catalysis.Lastly, vinyl cyclopropanols and cyclopropylcarbinols have been prepared by the cyclopropanation of enol silyl... 

The ODPM rearrangement is stereoselective with complete inversion at C-6. It is regioselective by the exclusive formation of the intermediate 79. The cyclopropanol rearrangement of 79 proceeds in a regioselective way with total inversion at the reaction centre, while cleavage of only one cyclopropane bond accounts for the regioselectivity. 

The anions of vinyl cyclopropanols (16), conveniently released from ethers (15) with BuLi, rearrange rapidly to cyclopentenes (17). 

An interesting application of a 1,2-disubstituted cyclopropanol in a seven-membered ring-annelation methodology has been developed by Cha et al. [82], The cyclopropanol 124, obtained from methyl 1-cyclopentenecarboxylate (123) and 4-(triisopropylsilyloxy)-butylmagnesium chloride, was converted to a 1,2-dialkenylcyclopropanol bis-silyl ether, which, by a subsequent facile Cope rearrangement, afforded the cycloheptadiene-anne-lated cyclopentane derivative 125 in 32% overall yield (Scheme 11.32). 

A hitherto unknown type of rearrangement of l-(l-alkynyl)cyclopropanols (321) to cyclopent-2-en-l-ones (322) mediated by octacarbonyldicobalt" and hexacarbonyldicobalt" complexes has been described. A possible pathway for the transformation is outlined in Scheme 101. A -proton transfer accompanied by a metal-mediated Stevens rearrangement, which converts a coordinated dimethylsulfane... 

Hydroxymethylenecyclopropanols (340) have been shown" to be intermediates in the photochemical rearrangement of a, -unsaturated carbonyl compounds (339) to 1,4-dicarbonyl compounds (341). The products are eventually obtained by double tautomerization of the enol and cyclopropanol portions of (340). 

All the reactions described so far are carried out using stoichiometric amounts of Co2(CO)8. However, a coordinatively unsaturated 02(00)5 species would be liberated when the rearrangement proceeds, and if this cobalt species could form an alkyne-Co2(CO)6 complex with another molecule of 1-(1-alkynyl) cyclopropanol, the reaction should proceed with only a catalytic amount of 02(00)8 [13, 18]. In practice, when 1-phenylethynylcyclopropanol (11b) is treated with a 10 or 20 mol% amount of 02(00)8, the rearranged product 13b is obtained in 43 and 59 % yield, respectively. Thus, the reaction in fact proceeds with a catalytic amount of 02(00)8 however, the efficiency is low and a complex mixture of by-products is also obtained. As this low efficiency could be ascribed to instability of the unsaturated cobalt species, the catalytic reaction could be made more efficient by the addition of a stabilizing additive. 

Condensation of /3-(hydroxyalkyl)cyclopropanols with aldehydes, followed by rearrangement of acetals formed (Scheme 27), is proposed as simple and convenient method for the synthesis of c -2,7-disubstituted oxepan-4-ones <20050L515>. Though the intermediate acetal could be isolated in some cases, the reaction is usually carried out as one-pot procedure with sequential addition of two Lewis acids, Al(OTf)2 and TiCl4. The overall yields range from 50% to 70%. 

The vinylcyclopropane to cyclopentene rearrangement is seemingly broadly applicable to solution of the five-ring annulation problem. Besides the example cited in Scheme 8, routes provided by Trost,61 Miller,62a and Conia62b are conceptually attractive. Thus, we see that reaction of a cyclopentanone with the cyclopro-pyldiphenylsulfonium ylide provides an oxaspiropentane which can be opened efficiently with an amide base (Scheme 10). The resulting silylated cyclopropanol can be... 

---