NOVEL ROUTES TO ENOL ETHERS, UNSYMMETRICAL KETONES, ALPHA-BROMOALKYL KETONES, 1,4-DIKETONES, 2-ETHOXY-2-CYCLOPENTENONES, AND ALPHA-KETO ENAMINES

Highly regioselective S(N)2' reactions of adducts 6 (readily prepared by reactions of halides with the allyl anion 12 of 11) with Grignard reagents gave enol ethers 13, which were converted (in one-pot reactions from 11) into ketones 14 and alpha-bromoalkyl ketones 15 in good yields. The monoprotected 1,4-diketone derivative 16 (prepared by Michael addition of the allyl anion 12 with methyl vinyl ketone) was converted both into 1,4-diketones 18 and into protected gamma-hydroxyalkyl ketone 20 by selective Grignard reactions, which could be directed either to the carbonyl, or the protected propenoyl, or to both functionalities. The allyl anion 12 with alpha-substituted acetic esters gave alpha-acylated adducts 24, which underwent in situ unfavored endo-trig cyclization upon treatment with NaH and secondary amines, to give 2-ethoxy-2-cyclopentenones 27 and 28 and alpha-keto enamines 25 in good yield. The mechanism for the cyclization is discussed.