ISSN:
1042-7163
Keywords:
Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A series of thiophene dioxides (3), including highly congested ones, were synthesized. Their oxidation with m-chloroperbenzoic acid (m-CPBA) was investigated either in the presence or in the absence of Na2CO3. The following conclusions were reached. (1) Oxidation in the presence of Na2CO3 affords the corresponding epoxides (4) in moderate to excellent yields. (2) Oxidation in the absence of Na2CO3 produces the ring-contracted thiete 1,1-dioxides (5) as the principal product, thus providing a novel synthesis of the sulfur-containing unsaturated four-membered ring system. If necessary, 5 can also be derived by treatment of 4 with BF3·Et2O. In an extreme case, the oxidation of 3,4-di(1-adamantyl)thiophene afforded the corresponding thiete dioxide 5b directly in 78% yield. (3) Oxidation takes place faster with a more congested 3, probably because of destabilization of the HOMO by steric repulsion between bulky substituents and also owing to relief of steric crowding on going from the ground to the transition state. (4) The formation of 5 from 3 in the absence of Na2CO3 can be explained by the occurrence of an acid-catalyzed rearrangement of 4 initially formed. However, a competitive pathway leading directly to 5 may also be operative.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hc.520040506
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