Dialkenyl carbinols

Epoxidation of Prochiral Dialkenyl Carbinols and of meso-Secondary Diallylic Alcohols... 

Epoxidation of prochiral dialkenyl carbinols 28 provides the anti-epoxide 29 of extremely high optical purity [68, 69, 70]. The first epoxidation occurs in an enantiotopic selective manner while the second one proceeds in an enantiomer-differentiating manner (kinetic resolution). In the second step, the minor (R)-monoepoxides 30 are consumed faster than the major (S)-enantiomers 29 and therefore the enantiomeric excess of the major anfi-monoepoxide 29 increases as the reaction proceeds. If a reaction proceeds with a kfas(/ksio, =104, anti-syn selectivity for the fast reaction=98 2 and for the slow reaction=38 62, as observed in the epoxidation of racemic ( )-l-cyclohexyl-2-buten-l-ol,the enantiomeric excess of anti-29 on calculation is 99.4,99.96, and 99.994% ee at 50,99, and 99.9% conversion, respectively. Yields of anti-29 are 48,93 (maximum), and 91% at the respective conversions. Actually, in the epoxidation of 1,4-pentadien-... 

Mixed carbonates of unsymmetrical dialkenyl carbinols undergo ipj osubstitution to afford chiral aryl ethers, with high degrees of regioselectivity and enantioselectivity when catalyzed by a Pd(0)-complex of 297... 

Parker has studied the regiochemical outcome of the Meerwein-Eschenmoser Claisen rearrangement in dialkenyl carbinols (296 and 297) and the realated propargyl-alkenyl carbinol (300) system. The less substituted alkene participated in the rearrangement (e.g., 298), and the process differentiated between an alkene and an alkyne resulting in the formation of enyne amide 301. ° ... 

A simple and efficient method for the stereochemical control of consecutive stereogenic center construction has been realized [16] by utilizing hydroboration of dialkenyl carbinol derivative. Consequently, hydroboration of 15 with 9-BBN, followed by alkaline oxidation yields 90% of anti, anti-isomer 16, whereas ThxBHj affords syn, anti-isomer 17 in 62% yield (Chart 6.27) [16]. 

After modification of the hydroxy group with an enantiopure ferrocenylphosphino-directing ester group, the resulting chiral dialkenyl-carbinols could be desymmetrized by using an achiral rhodium catalyst in almost perfect optical purity (Scheme 4.111) [22]. Removal of the directing auxiliary was... 

Scheme 4.111 Desymmetrizing hydroformylation of dialkenyl carbinols with the assistance of a chiral directing group (in the original paper, some transformations have been carried out with the corresponding enantiomers).

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