P-Toluenesulfonic acid halides

In what might be viewed as a variation on the ionic hydrogenation theme, this same Russian group has found that the combination of zinc/aluminum halide/p-toluenesulfonic acid reduces 2-alkylthiophenes mainly to the tetrahydro derivatives (equation 30). The minor product, 2-alkyl-2,5-dihydrothiophene, is... 

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