27/-Benzo thietes cycloaddition

The catalysed macrocyclization of thietanes by metal carbonyl complexes has been reviewed <00ACR171>. Electronically stabilized thiones have been shown to undergo [2+2] cycloaddition with benzyne to give 27/-benzo[i>]thietes, for example 6 <00BCJ155>. 

The 8 + 2-cycloaddition of 2//-cy c I o h cpta[h ] furan -2 - one (155) with acyclic 1,3-dienes provides a facile route to bicyclo[5.3.0] ring systems (156) (Scheme 61).291 2H-Benzo[Z>]thiete in the o-quinoid form undergoes 8 + 2-cycloaddition with 1,3-dithiolane-2-thione, l,3-dithiole-2-thiones, and adamantanethione to produce 4//-1,3-benzoditliianes.292... 

The reactivity of the benzo analogue of compound 41, that is, 2//-naphtho[l,2-4]thiete 47, has also been studied. Cycloaddition reactions with dienophiles or heterodienophiles performed in boiling toluene yielded naphtho-condensed sulfur heterocycles (Scheme 5) <1998JHC1505>. 

Benzyne generated at room temperature from phenyl[2-(trimethylsilyl)phenyl]iodonium trifluoromethanesulfo-nate has been trapped in a [4+2] cycloaddition reaction with diarylthiones. The initial product, a 6-aryl-477 dibenzo[, r/]thiopyran, is accompanied by 6-aryl-67/-dibenzo[, r/]thiopyran arising by 1,3-prototropic aromatization of the cycloadduct (Equation 114). The use of sterically congested thiones, such as thiopivalophenones, results in competition from a [2+2] cycloaddition and 2/7-benzo[A]thietes are the sole products <2000BCJ155>. 

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