The reactions of solutions of 2,2-ditipylethene-1,1-diol (tipyl = 2,4,6-triisopropylphenyl) (1), which is the enol of ditipylacetic acid, were studied. Oxidation with (p-BrC6H4)3N•+SbCl6- gave a benzofuranone, i.e., a five-membered lactone (5) by cyclization via the oxygen on the ring, and ketonization with loss of aromaticity of the ring. Bromination also gave 5, presumably via an initial oxidation of the oxygen, as well as a bromine-containing six-membered lactone, a benzopyranone (9), formed by cyclization on an o-i-Pr group and ring bromination. No product resulting from reaction of bromine with the double bond was formed. This is ascribed to shielding of the double bond by steric crowding. Attempted etherification of the enolic OH groups did not give the ketene trimethylsilyl or methyl acetals. With diazomethane a bicyclic trienone 13 was formed, presumably by cyclopropanation of the ditipylketene (2) which is in equilibrium with 1, followed by a vinyl cyclopropanone rearrangement to 13. The formatio...