[2 pi+2 sigma] and [8 pi+2 sigma] types cycloaddition reactions of aza-, thio-, and thiaza-azulen-2(1H) -one derivatives with naphtho[b]cyclopropene: Effects of solvents and ytterbium complex

Reactions of naphtho[b]cyclopropene with 1-aza- or 1-thiaazulene-2(1H)-one derivatives in chloroform under the presence of a catalytic amount of ytterbium complex afforded [2pi + 2sigma] type cycloaddition products. The analogous reactions of the cyclopropene with a 1-thia-3-azaazulene-2(1H)-one derivative gave an [8pi + 2sigma] type cycloadduct. These reactions were considered to proceed via ionic processes, in which the azulene-2(1H)-one derivatives played as 2pi and 8pi components, respectively. On the other hand, reactions of the cyclopropene with 1-azaazulene-2(1 H)-one derivatives in benzene yielded the another type of [8pi + 2sigma] type cycloadducts via a concerted process.