Vinyl cyclopropane-cyclopentene rearrangement

On the other hand, Rh1 in the absence of CO leads to 12 [12] formed via a vinyl cyclopropane/cyclopentene rearrangement. Such a rearrangement without a catalyst would require temperatures between 300 and 400 °C ... 

Use of chiral cyclopropylethynyllithium derivatives permits the elegant selective synthesis of labeled chiral vinylcyclopropanes, for stereochemical studies of the thermal vinyl cyclopropane-cyclopentene rearrangement. Thus, reductive elimination of (15, rra )-(2,2-dibromoethenyl)-l-methylcyclopropane with BuLi in pentane, followed by hydrolysis of the lithium acetylide, afforded (15, rraw5)-2-ethynylmethylcyclopropane (equation 157). 

Small amounts of cyclopentene derivatives are detected in cyclopropanation reactions of electron-deficient dienes, but they may result from thermal rearrangement of the corresponding vinyl cyclopropanes and not from a direct [4+1] cycloaddition... 

One of the classical papers in this area is Neureiter s discovery of the vinyl-cyclopropane to cyclopentene rearrangement [185]. This important process was first observed on a l,l-dichloro-2-vinylcyclopropane derivative, which on heating yielded a chlorocyclopentadiene, presumably by the loss of hydrochloric acid from the initially formed 4,4-dichlorocyclopentene. 

Cyclopentene annelation. The known rearrangement of vinyl cyclopropanes to cyclopentenes (cf. 7, 190 9, 83, 265) can be used to obtain silyl-substituted cyclopentenes. The precursors, (l-trimethylsilylcyclopropyl)ethylenes (2), are usually prepared by addition of 1 to an aldehyde or a ketone followed by cyclopropanation (C2HjZnI, CH2I2) of the adduct. The products are then dehydrated by TsOH to 2 (equation I).1... 

These silyl-substituted vinyl cyclopropanes are stable to acid but rearrange thermally to silyl-substituted cyclopentenes in which the double bond occupies the more substituted position.2 Example ... 

This reaction does not create a ring but there is an important group of sigmatropic rearrangements that make five-membered rings—the vinyl cyclopropane to cyclopentene rearrangement. 

On the basis of triplet sensitization experiments, this rearrangement was shown to occur from the excited singlet state and to involve the biradical intermediate 111. Interestingly, vinyl cyclopropane esters 113-114 underwent geometric isomerization at a much faster rate than rearrangement on direct excitation (Scheme 8.34) [57, 58]. However, the triplet-sensitized reaction of these esters give both cyclopentene and isomerization products. 

The pyrolysis of vinylcyclopropanes 78 to 79 was accompanied by the competing vinyl-cyclopropane to cyclopentene rearrangement, which furnished sesquiterpene intermediates 80.8 ... 

The utility of the Chugaev elimination for the formation of olefins without rearrangement of the carbon skeleton can be observed upon pyrolysis of the xanthate of alcohol 14.17 The desired vinyl cyclopropane (IS) was isolated in reasonable yield (42%) along with a small amount of the rearranged xanthate. Alternatively, acid-mediated dehydration with sulphuric acid yielded a variety of rearranged products in low yield. Ester pyrolysis (of the acetate of 14) also furnished a variety of compounds, with the major product being cyclopentene 16. 

In addition to the two- and three-component entries to five-membered rings in Scheme 3-39, the nickel-catalyzed rearrangement of vinyl cyclopropanes to cyclopentenes has also been developed. Whereas various catalysts promote the rearrangement of vinyl cyclopropanes under harsh conditions, nickel-iV-heterocyclic carbene (NHC) complexes were found to catalyze the rearrangement under mild conditions with relatively broad scope (Scheme 3-40). ... 

Thermal Reactions.—Vinylcyclopropanes and Related Compounds. The vinyl-cyclopropane rearrangement " provides a convenient method for cyclopentene ring formation even in highly constrained ring-fused systems. A trans-... 

Professor Lambert established (J. Am. Chem. Soc. 2009,131,2496) that the rearrangement of the vinyl cyclopropane 29 to the cyclopentene 30, usually a high temperatare process, could be effected with Mgl. We (J. Org. Chem. 2009, 74, 2433) found that Fe-mediated cyclocarbonylationof31 led to the cyclohexenone 32. 

Vinyl-substituted cyclopropanes undergo thermal rearrangement to yield cyclopentenes. Propose a mechanism for the reaction, and identify the pericyclic process involved. 

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