A. 690 5H-Cycloprop[f]isobenzofuran (6) and the sulfur analogue 5H-cyclopropa[f][2]benzothiophen (18) have been prepared by a sequence of reactions involving trapping of 1,2-dibromocyclopropene with 3,4dimethylidenetetrahydrofuran and 3,4dimethylidenetetrahydrothiophen foiiowed by sequential dehydrogenation and di-dehydrobromination. Both cyclopropa-fused heterocycles, like their parents, have limited stability. Several other 5,6-methylene-bridged and 5,6-disubstituted isobenzofurans (32) have been generated and characterized as their adducts with dimethyl fumarate. Second-order rate constants for the reaction of dimethyl fumarate with isobenzofuran, 5H-cycloprop[f]isobenzofuran as well as the series of substituted derivatives have been measured. The reactivity span is only one order of magnitude suggesting that T-bond fixation (the Mills-Nixon effect) does not play a significant role in determining the reactivity of (6).
154ChemInform Abstract The cyclopropane (I) reacts with tetrabutylammonium fluoride to give the dibromocyclopropene (II). 2,3-Bis(iodomethyl)butadiene (III) is cyclized to form the furan or thiophene derivative (IV) which undergo Diels-Alder reaction with (II), forming the cycloadducts (V). Oxidation and dehydrobromination produce the aromatic compounds (VII). (VIIa) and dimethyl fumarate (VIII) yield the adduct (IX).
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