2-Vinylbenzo furans

Multi-ring heteroaromatic compounds containing furan and thiophene rings have been prepared by pressured cycloaddition of 2-vinylbenzo[ ]furan (40a) and 2-vinylbenzo[Z)]thiophene (40b) with 3-nitro-2-cyclohexen-l-one (41) and 2-inden-l-one (42), respectively, generated in situ. ... 

As vinylbenzofurans allow a large variety of substituted dibenzofurans to be synthesized, 2- and 3-vinylbenzo[b]thiophenes allow an easy entry, by Diels Alder reaction with the appropriate dienophiles, to substituted dibenzo-thiophenes which are not easily accessible by other methods. Vinylbenzo-[bjthiophenes are less reactive than the corresponding vinylbenzo[b]furans. Some cycloaddition reactions of 2-vinylbenzo[b]thiophene (82) with various dienophiles are reported [83] in Scheme 2.34. 

Benzo[6]furan and 2-methylbenzo[6]furan fail to undergo photooxygenation but 2,3-dimethyIbenzo[6]furan yields 2-acetoxyacetophenone (364). At -78 °C the peroxide (363) is produced which at higher temperature rearranges to the acetophenone (364 Scheme 98). 2-Vinylbenzo[6 Jfurans, e.g. trans- 2- styrylbenzo[6 Jfuran (365 Scheme 99), yield photooxides which may be isolated. Compound (366) on treatment with a catalytic amount of triethylamine yields the lactone (367) (77BCJ3026). 

Benzyne in solution reacts as a dienophile Wittig (1957) first demonstrated this in the reaction of benzyne with furan. Corbett and Porter (1965) obtained further supporting evidence by isolating 1,4-addition products from benzyne with 1-vinylnaphthalene and 3-vinylbenzo[b]-thiophene Dilling (1966) did the same with styrene. 

Vinylbenzo[7]furans, 3-vinylfuropyridines, and 3-vinylindoles were employed as conjugated dienes in the Diels-Alder reaction with ethyl acrylate, affording tricyclic adducts in fair to good yields, as shown in Equation (103) <20020L2791>. 

Vinylbenzo[l)]furans were synthesized via copper-catalyzed one-pot, three-component reactions of o-iodophenols, in situ generated aUenes, and dichloromethane (14OL5160). 

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