The irradiation of a cyclic b-dicarbonyl iodonium ylide with 1,3-diene in acetonitrile gives substituted dihydrofurans in moderate to high yields, presumably via a stepwise mechanism.Iodonium ylides 1 are considered as synthetic equivalents of the corresponding diazo compounds, without major drawbacks such as explosion, toxicity, and/or carcinogenicity. Furthermore, b-dicarbonyl and b-disulfonyl iodonium ylides are readily prepared 2,3 in high yields from the related active methylene compounds and a hypervalent iodine precursor. The photochemical and/or metal-catalyzed decomposition of these stable iodonium ylides generated reactive intermediates, which undergo several types of reactions, i.e. transylidation 1 with various nucleophiles, cycloaddition reactions leading either to the formation of cyclopropanes 3,4 or five-membered heterocycles 5 , etc.Following our studies directed towards the development of new synthetic applications of iodonium ylides 6 , we thought that heavily substituted dihydrofurans could be easily obtained by the reaction of a b-dicarbonyl iodonium ylide and a conjugated diene. The use of 1,3-diene has been emerging from the point of view that an extra double bond moiety in the dihydrofuran could lead to further interesting transformations, as well as that the presence of this extra olefinic moiety should influence the behaviour of the reacting double bond. We have previously published 6a,d the synthesis of dihydrofurans starting from iodonium ylide 1a and alkenes. Based on these results, we now wish to report the synthesis of 1,5-dienes 3 by the reaction of iodonium ylides 1a,b with 1,3-dienes 2.Irradiation of a suspension of iodonium ylide 1a, and 1,3-diene 2a in CH 3 CN for 60 min at room temperature afforded 7 dihydrofuran 8 3a in 83% yield (Scheme 1). The reaction was extended to iodonium ylide 1b and a variety of 1,3-dienes 2b-f, which underwent facile cycloadditions, affording the related dihydrofurans 3 in moderate to excellent yields (Table). When the reactions were repeated thermally, in the presence of catalytic amounts of Cu(acac) 2 , complex mixtures of inseparable products were isolated instead.It is noteworthy that the reaction proceeds without the use of an inert atmosphere. Acyclic 2a-d, with varied degree Scheme 1Downloaded by: University of Arizona Library. Copyrighted material.
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