Electroreduction of 2,2,5,5-tetramethylcyclohexane-1,3-dione on mercury

Clemmensen reduction. Part 7. Acid-catalysed opening of cyclopropane-l,2-diols

“…In only one case was evidence obtained for the opening of a cyclopropane-1,2-dio1 to give a p-ketol. 1,3-Dimethyl-2-phenylcyclopropane-1,2-diol (7) gave, with 4 mol 1-1 acid, the now expected product (27) and a small amount of the enone (28); this latter compound must arise by dehydration of a p-ketol. When difference in results depending on the acid concentration suggests that protonation at the non-oxygenated C-3 is of major importance in initiating carbon-carbon bond cleavage in strong acid; in dilute acid, however, the mesomeric effect of the oxygen atom of a non-protonated hydroxy-group assumes the dominant function in ' pushing ' the ring open.…”

“…1,3-Dimethyl-2-phenylcyclopro~ane-1,2-diol (7). Rearrangement of the diol ( 7) by heating i t under reflux for 2 h gave : (i) 3-1nethyl-4-phenylbut-3-en-2-one (28) (9%) v, , , ~ 1 670 ( G O ) and 1 615 cm-l (C=C); 8g 2.00 (3 H , d, J ca.…”

“…(7) was treated with more dilute acid (0.1 moll-l) the enone (28) became the major product. The Clemmensen reduction of the corresponding diketone, in 5 mol 1-1 acid, gave only the a-ketol (27) and its corresponding deoxy-ketone.…”