No abstract

Abstract

The cyclization of the α-iodo mixed acetals derived from properly substituted cyclohexenols , a process which has already been shown to permit the stereoselective and regioselective introduction of a different carbon chain at each of the termini of the allylic double bond, may be used for the construction of trans hydrindans suitable for further elaboration to steroids. In one particular instance, the process involves the formation of four new carbon-carbon bonds in a single operation.

The first activation parameter data for the reaction of dimethyldioxirane (1) with five cis/trans pairs of alkenes are reported. The epoxidation of cis-1,2-dialkylalkenes (2cis: R 1 = Me, R 2 = iPr; 3cis: R 1 = Me, R 2 = tBu; 4cis: R 1 = R 2 = Et; 5cis: R 1 = Et, R 2 = iPr; 6cis: R 1 = Et, R 2 = tBu) and trans-1,2-dialkylalkenes (2trans: R 1 = Me, R 2 = iPr; 3trans: R 1 = Me, R 2 = tBu; 4trans: R 1 = R 2 = Et; 5trans: R 1 = Et, R 2 = iPr; 6trans: R 1 = Et, R 2 = tBu) by 1 produced the corresponding epoxides, quantitatively and stereospecifically, as the sole observable products. Activation parameters of the epoxidation of the five pairs of alkenes, 2cis-6cis and 2trans-6trans, by 1 were determined using the Arrhenius method. Enhanced selectivity for cis-vs. trans-alkene epoxidation was observed at lower temperatures. In general, the ∆G ‡ terms were larger and

Abstract:The mono-epoxidation of geraniol by dimethyldioxirane was carried out in various solvents. In all cases, the product ratios for the 2,3 and 6,7 mono-epoxides were in agreement with literature values. Kinetic studies were carried out at 23 ºC in the following dried solvent systems: acetone (k 2 = 1.49 M -1 s -1 ), carbon tetrachloride/acetone (9/1, k 2 =2.19 M -1 s -1 ), and methanol/acetone (9/1, k 2 = 17 M -1 s -1 ). Individual k 2 values were calculated for epoxidation of the 2,3 and 6,7 positions in geraniol. The nonconjugated diene system was modeled employing two simple independent alkenes: 2-methyl-2-pentene and 3-methyl-2-buten-1-ol by determining the respective k 2 values for epoxidation in various solvents. The kinetic results for each independent alkene showed that the relative reactivity of the two epoxidation sites in geraniol as a function of solvent was not simply a summation of the independent alkene systems.