Cyclopropanols cyclobutanones

In contrast, propargylic cyclopropanols and cyclobntanols undergo ring expansion to form cyclobutanones and cyclopentanones with Au(I) catalysts (eqnation 10). 

As noted above, reactions of cyclopropanones with nucleophiles may yield intermediates such as vinyl cyclopropanols which are readily converted to cyclobutanones through carbinyl cations . In like manner, generation of electron-deficient nitrogen species may lead to the formation of ) -lactams by related ring enlargement Hydrazoic acid, amines and hydroxylamine derivatives have all been used in this context as shown in Scheme 12. These reactions are summarized in the examples outlined below. 

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... 

Cyclobutanols. Grignard reagents induce rearrangement of oxaspiropentanes to cyclobutanones which react further. Benzylic reagents provide some cyclopropanols. 

Oxaspiropentanes are prone to ring opening with or without concomitant opening or enlargement of the cyclopropane ring under acid or basic conditions. A number of oxaspiropentanes have therefore been prepared and reacted further to cyclopropanols or cyclobutanones without being... 

Bromination of methylenecyclopropane with A -bromosuccinimide in dimethyl sulfoxide in the presence of water afforded different products depending on the ratio methylenecyclopropane/ Wbromosuccinimide and the amount of water available. Two equivalents of iV-bromosuc-cinimide predominantly gave l-bromo-l-(bromomethyl)cyclopropane (80%) in addition to some cyclobutanone (20%) derived from 1-(bromomethyl)cyclopropanol (Table 1, entry 7). With equimolar amounts of the alkene and AT-bromosuccinimide in aqueous solution (Table 1, entry 8), the bromohydrin, 1-bromo-l-hydroxymethylcyclopropane, was formed as the main product (70%).The reaction conditions suggest the addition of a positively charged bromine rather than a radical mechanism. 

Cyclopropanols and their derivatives (ethers, esters) constitute the most important class of cyclopropanes which undergo this type of ring enlargement. Synthetically useful strategies to cyclobutanones have been devised based upon an efficient synthesis of appropriate cyclopropanols (see Sections 1.A.1.2.1.2. and 1.A.1.2.1.4.) or oxaspiropentanes. 

Vinylcyclopropanols also readily undergo thermal rearrangement to cyclobutanones. l-(Cyclo-pent-l-enyl)- and l-(cyclohex-l-enyl)cyclopropanols 41 were converted quantitatively to the... 

Corey employed the Kulinkovich reaction in the total synthesis of P-arianeosene (48). Ester 46 was converted to cyclopropanol 47, which served as the substrate to make cyclobutanone by treating 47 with Al(Me)3. 

Cyclobutanones have been prepared from vinylic cyclopropanols, and the unique ylids iS, prepared as shown, can be converted into a wide variety of carbocyclic systems. ... 

Cyclopropanol 74 underwent asymmetric ring expansion via 1,2-alkyl migration upon treatment with a chiral palladium catalyst to furnish the cyclobutanone... 

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