Cyclopropanol vinyl

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

On the other hand, solvolysis of the tosyl derivative of 1-cyclopropyl-cyclopropanol (112) in aqueous ethanol does not lead to ring enlarged products. 91 Apparently, the incipient cyclopropyl cation is better stabilized by conjugative interactions with another cyclopropyl system than with a vinyl group. 

On the other hand, l-(phenylethynyl)cyclopropanol 9 (R = Ph) underwent a C3 -> C4 ring expansion and subsequent decarboxylation when treated with MCPBA to yield the 2-phenylcyclobutanone 47, likely via the intermediate 2-(l-hydroxy-cyclopropyl)-2-phenyl ketene 44, formed by migration of the cyclopropyl group in the vinyl cation 43. The ketene 44 thus resulting could be attacked by a second equivalent of MCPBA and ring expanded to the (3-ketoacid 46 which would easily decarboxylate to yield 47, Eq. (15) 14>. 

In analogy to the preparation of the cyclopropanone hemiacetal 3 (vide supra, Eq. (1)7), reductive cyclization of the piperidide of 3-chloropropionic acid 193 with sodium in ether in the presence of ClSiMe3, gave the 1-piperidino-l-trimethylsilyloxy-cyclopropane 194 a which was converted to the cyclopropanol 194 b upon treatment with methanolic tetrabutylammonium fluoride. Both 194 a and 194 b can be used for the ready generation of cyclopropane derivatives thus the silyl ether 194a could be reacted directly with the vinylic Grignard reagents 195 to provide the vinyl cyclopropane derivative 196, (Eq. (61)128). 

Although it has been well known that cyclopropanols are cleaved by apt electrophiles, this process was only applied for synthetic purposes when good methods for the preparation of siloxycyclopropanes had been worked out. Murai and coworkers investigations demonstrate that transformations according to equation 69 using strong electrophiles lead to versatile products such as J -bromoketones , vinyl ketones or y-oxoesters. r ... 

Alkoxy-2-vinylcyclopropanes rearrange stereospecifically to 2-cyclopentenols under very mild conditions. Thus, the lithium salt of 2-vinyl-1-cyclopropanol (204) undergoes the vinylcyclopropane-cyclopentene rearrangement at room temperature (equation 137). ... 

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... 

Cyclopropanols afford alkyl cyclopropyl ethers on treatment with diazomethane, trial-kyloxonium tetrafluoroborate, tetrahydropyran, ethyl vinyl ether, or sodium hydride followed by iodomethane dimethyl sulfate has also been used. The yields are moderate to excellent. 

Addition of phenylselanyl bromide, in the presence of triethylamine, to a bicyclic vinyl-cyclopropanol 16 resulted in an electrophilically initiated ring expansion to the corresponding spirocyclobutanone 17 with high diastereomeric purity. This rearrangement forms the basis of the total synthesis of plumericin. 

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. ... 

In 2009, Chiba s group reported a manganese-mediated synthesis of pyridines from cyclopropanols with vinyl azides [70]. In the presence of 1.7 equivalents of Mn(AcAc)3, a variety of pyridine derivatives have been prepared in good yields at room temperature. In their further studies, they realized this transformation in a catalytic manner [71]. In their mechanistic studies, they found the reactions were initiated by a radical addition of /3-carbonyl radicals, generated by the one-electron oxidation of cyclopropanols with Mn(III), to vinyl azides to give imi-nyl radicals, which cyclized with the intramolecular carbonyl groups. Additionally, the application of this newly developed methodology in the synthesis of quaternary indole alkaloid, melinonine-E, was accomplished as well (Scheme 3.33). 

Scheme 3. S3 Mmcatalyzed synthesis of pyridines from cyclopropanols with vinyl azides.

---