Steve Feiner

Investigations on the question of multiple mechanisms in the cope rearrangement

Abstract The possible occurrence of the ionic Cope rearrangement, and other non-concerted mechanisms is discussed. The synthesis of 2 - (1 - ethyl - 1 - propenyl) -2- (3 - p - methoxyphenylallyl)malononitrile (1b) and its clean thermal 1,3 rearrangement to (1 - ethyl - 5 - p - methoxyphenyl - 2 - methyl - 4 - pentenylidene)malononitrile (4) are reported. This result contrasts with the rearrangement of 2 - (1,1 - dideuterioallyl) - 2 -(1 - ethyl - 1 - propenyl)malononitrile (1c) which isomerizes cleanly in a 3,3 rearrangement. Rearrangement of 2 - (1 - cyclohexenyl) - 2 - (3 - p - methoxyphenylallyl)malononitrile (11), however, leads sluggishly to [2 - (p - methoxy - α - vinylbenzyl)cyclohexylidene]malononitrile (19) (3,3 shift) and rearrangement of 2 - (1 - isopropyl - 2 - methyl - 1 - propenyl) - 2 -(3 - p - methoxyphenylallyl)malononitrile (12) leads, also slowly, to (1 - isopropyl - 5-p- methoxyphenyl - 2,2 - dimethyl - 4 - pentenylidene)malononitrile (14) (1,3 shift). Rearrangement of 1b in the presence of sodium borohydride allows interception of the proposed ionic intermediates and isolation of 2 - (1 - ethylpropylidene)malononitrile (5) and anethole (21c). Ion trapping experiments also gave positive results in the 3,3 rearrangement of 11. These results are discussed in terms of the ionic Cope rearrangement.

The chemistry of 2-methyltetrahydropyran-4-one: An L-Selectride reaction that gives predominantly the equatorial alcohol

The stereoisomers of 2-methyltetrahydropyran-4-ol have been separated and identified by carbon-13 and proton nmr analysis of the trideuteriomethyl-2,6,6-trideuterio analogue. Stereoisomeric product ratios of reduction of 2-methyltetrahydropyran-4-one (1) by NaBH4, KBH4, L-Selectride, K-Selectride, and LiBH(nBu)3 have been determined and compared with reductions of 3-methylcyclohexanone. Product ratios in the reduction of the two substrates by the borohydride reducing agents are similar but are quite different in the reduction by the Selectride reducing agents, 1 being reduced by Selectride to give 73% equatorialalcohol. Two possible mechanisms of reduction of 1 are proposed, involving intramolecular assistance by the cyclic ether oxygen.

The lack of allylic oxidation in the moffatt oxidation. Preparation of 5α-lanost-8-en-3-one.

Abstract The Moffatt oxidation (dimethyl sulfoxide-dicyclohexylcarbodiimide) is successful in oxidizing 5α-lanost-8-en-3β-01 (I) to 5α-lanost-8-en-3-one (II) without any detectable trace of the usual competing allylic oxidation products.