ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The cation radical vinylcyclobutane (VCB) rearrangement is found to be a reaction of substantial scope, synthetic utility, and exceptional kinetic facility. In conjuction with cation radical cyclobutanation, it constitutes an effective method for net (indirect) Diels-Alder addition to electron rich dienophiles. Reactions can be carried out with either aminium salt or photosensitized electron transfer (PET) initiation and are powerfully facilitated by ionizable substituents such as p-anisyl, phenylthio, and phenoxy at the 2-position of the vinylcyclobutane. The intramolecularity of the reaction is clearly established and in four discrete systems preferred sr (suprafacial/retention) stereochemistry is observed. A theoretical basis for sr stereochemistry in the cation radical VCB rearrangement is advanced. The transition state for the reaction is considered to be similar to that for the direct cation radical Diels-Alder cycloaddition, another cation radical pericyclic reaction which converges on the same product. This model of the VCB rearrangement transition state is used to rationalize the strong rate-retarding effect of a Z-methyl substituent attached to the vinyl group and of a methyl substituent at the 4-position of the vinylcyclobutane ring cis to the vinyl substituent.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610020108
