Cyclisation of phenol- and enol-acetylenes: syntheses of 2,3-dihydro-2-methylene-1,4-benzodioxins and -1,4-benzoxazines

In the presence of yellow mercuric oxide, pyrocatecol mono(prop-2-ynyl) ether and its analogues were cyclised to afford 2,3-dihydro-2-methylene-1,4-benzodioxins. o-(N-Substituted-N-prop-2-ynyl)aminophenols were also cyclised to 2,3-dihydro-2-methylene-1,4-benzoxazines in good yield. In contrast, enol-acetylenes, such as 2-benzoyl-1-oxo-1-phenylpent-4-yne, gave 2,3,5-trisubstituted furans.