Vinylcyclobutane Rearrangements

The vinylcyclobutane rearrangement serves as a novel [3 + 3] or [4 + 2] strategy for six membered ring formation depending upon whether a nucleophilic (Eq. 96) or electrophilic (Eq. 97) conjunctive cyclopropyl reagent is employed. The use of the... 

Diels-alder adducts at 0°C. This cation radical-vinylcyclobutane rearrangement is non-stereospecific, thus accounting for the formation of a cis-trans mixture of Diels-Alder adducts. Kinetic studies revealed (Scheme 8) that the ionization of these ethers involves an inner-sphere electron-transfer mechanism involving strong covalent (electrophilic) attachment to the substrate via oxygen (oxonium ion) or carbon (carbocation). 

Useful examples of the cyclohexene to vinylcyclobutane rearrangement for preparative purposes are given in Section 4.2.3. 

Examples 5 and 8 both involve vinylcyclobutane moieties. An interesting vinylcyclobutane rearrangement leading to novel spiro compound 11 was observed when cyclobutene trimer 10 was reacted with cesium fluoride in dimethylformamide at room temperature.37-38 Possible mechanisms for this unique isomerization have been proposed.38... 

Recent reviews by Baldwin" " " summarize the experimental and theoretical approaches to the vinylcyclopropane and vinylcyclobutane rearrangements. It is... 

The accelerated vinylcyclobutane rearrangement functions as the key step in several useful strategies for the assembly of functionalized six-membered carbocycles. As outlined in Scheme 21, these strategies are conveniently classified according to the approach used to synthesize the pivotal vinylcyclobutanol intermediate. 

Efficient and facile rearrangements analogous to the cation radical vinylcyclobutane rearrangement have also be identified in the vinylcyclopropane (VCP) series (Scheme 49). 

Oxyanion-accelerated rearrangement cf2-vinylcyclobutanol derivatives 8.33.13 Oxyanion-accelerated rearrangement cfl-vinylcyclobutanol derivatives 8.33.1.4 Azaanion-accelerated vinylcyclobutane rearrangements... 

The conclusion would appear to be that the vinylcyclobutane rearrangement involves biradicals, possibly formed by conrotatory-level motions (see Chapter 7, Section 3.14), Scheme 7.103, which are incompletely equilibrated before cyclization to cyclohexene because there is always a preference for utilization of the allylic moiety in a suprafacial way. 

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