Cyclohexenol isomerization

The catalytic system has been successfully extended to polymer-bound lithium amide co-bases of type 65 (see Table 4) which, like C—Li bases of type 63 and 64, are efficient regenerating agents of HCLA and poorly reactive toward oxiranes. For instance, the isomerization of cyclohexene oxide by 0.05 equiv of HCLA 55 in the presence of 1.45 equiv of 65 affords ( l-cyclohexenol in 92% ee (entry 15). It is of interest to note that, similarly to co-bases 63 and 64, the use of 65 leads to an increase of selectivity compared to the stoichiometric reaction at room temperature (Table 2, entry. ... 

The most general synthetic route to benzene oxides-oxepins is that initially developed by Vogel for 1. 1,4-cyclohexadienes (readily available from [2+4] cycloaddition of alkynes and butadienes, lithium-ammonia reduction of arenes, or dehydration of cyclohexenols) were converted to dibromoepoxides, the immediate precursors of benzene oxides. Modifications of this route have been used to prepare Ic and Id. Treatment of the monosubstituted arene oxide 43 (Figure 3) with (Et)4NF or thermal isomerization of 3-oxaquadricyclane provide additional synthetic routes to la. Similarly, the thermal (or photochemical) isomerization of the monoepoxide of Dewar benzene yielded la. ... 

H, A. Smith University of Tennessee)-. Dr. Siegel (Lecture 4) suggests that his experiments indicate that a cyclohexene-type intermediate is formed in the catalytic hydrogenation of benzene. Further evidence for this is found in the hydrogenation of phenols, for when these are reduced under a variety of conditions and over a number of catalysts, cyclohexanone is formed as an intermediate and is readily isolated. The best explanation for this appears to be the addition of two moles of hydrogen per mole of phenol to form a cyclohexenol which isomerizes to cyclohexanone before further hydrogenation takes place. The cyclohexanone is desorbed from the catalyst, and may be subsequently reduced to cyclohexanol. 

When isomerization of an allylic alcohol can lead to geometrically isomeric products, both geometrical isomers are generally among the kinetically controlled products. This has been demonstrated for isomerizations of a-methyl-allyl alcohol -, the 5-methyl-2-cyclohexenols -, a-ethynyl-y-methyl-allyl alcohoP, and a-ethynyl-a-methylallyl alcohof and is probably generally... 

Transition state for syn isomerization of cyclohexene oxide to allylic cyclohexenol. (Adapted from reference 58.)... 

Smdies of the oxidation of deuteriated 2-cyclohexenol provided some surprises. First, the rate expression for oxidation was not the rate expression for Wacker oxidation of acyclic olefins. Rather, it was the same form (Eq. 2) as that observed for isomerization of deuteriated aUyl alcohol at high [Cl ]. Second, as shown in Scheme 16, the deuterium distributions from the two deuteriated isomers, 14a and 14b, are consistent only with anti addition if the hydroxyl group is directing the Pd(ll) to the same side of the ring as the hydroxyl group. 

Scheme 11.6 Biocatalytic cascade isomerization of cyclohexenol into cyclohexanone by an ADH/ ER system. Undesired side reaction (reduction of cyclohexanone into cyclohexanol) is shown with a dashed arrow.

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