REGIOSELECTIVITY IN GAS-PHASE ELIMINATION-REACTIONS - 1,2 VS 1,4 AND ALLENIC ION VS DIENIDE FORMATION

Gas-phase elimination reactions of deuterium labeled 1-allyl-1-methoxy-6,6-dimethyl-2-cyclohexene (1), 1-methoxy-4,4-dimethyl-1-vinyl-2-cyclohexene (2) and 3-methoxy-3-methyl-1-butene (3) have been investigated. 1,2-Elimination is the favored pathway when 1 reacts with hydroxide (3.5:1) and methoxide (2.6:1), but 1,4-elimination is preferred with fluoride by 2:1. Abstraction of a vinyl proton is the elimination reactions of 2 and 3 is dominant when amide and/or dimethylamide are used, whereas the loss of an alkyl proton is heavily favored with hydroxide.