Reactions of cyclic β-keto esters and other enol derivatives with 3-acetoxyamino-2-isopropylquinazolin-4(3H)-one: further oxidation of the cyclic α-(3,4-dihydro-2-isopropyl-4-oxoquinazolin-3-yl)amino ketones with lead tetraacetate leading to ring-expansion (in dichloromethane) and ring-cleavage (in methanol)
The cyclic β-keto esters 12, 20, 22, 26, the β-diketone 28 and the enol silyl ethers 24 and 30 have been converted in 60–77% yields into the corresponding α-(oxoquinazolinyl)amino cyclic ketone derivatives 16, 21, 23, 29, 27, 25 and 31, respectively, by reaction with 3-acetoxyamino-2-isopropylquinazolin-4(3H)-one 11. Further oxidation of some of these products with lead tetraacetate gives products whose nature depends on the solvent used; in dichloromethane, 16, 21 and 25, which contain 5-membered ring ketones, give ring-expanded products 32, 38 and 39, respectively whereas, in methanol, ring-cleavage of 16, 25 and 27 occurs to give imino-esters 41, 44 and 42/43, respectively. Ring-expansion of 23, 27 and 31, which contain 6-membered ring ketones, does not occur and the only isolated product in each case is the benzoxazinone 40. A mechanism which accounts for this dependence on the solvent is presented: radical intermediates do not appear to be implicated.