Allyl cyclohexenyl ether

As is readily noted from the results summarized in Table 8E.13, enantioselectivity is very sensitive to a variety of factors such as the nucleophile and the nature of the allylic system as well as the ligand used. As expected, the enantioselectivity varied greatly with the structure of the nucleophile. Higher enantioselectivities were consistently obtained from the reactions of 2-cyclopentenyl phenyl ether than from the corresponding reactions of 2-cyclohexenyl ether. The biphenyl-derived DiPHEMP (7a) proved to be more effective than closely related BINAP (4) for this reaction. 

Rearrangements of allylic ethers can follow several pathways (Scheme 1). The 2,3- and 1,4-routes are symmetry allowed concerted processes, whereas the 1,2- and 3,4-rearrangements proceed in a stepwise manner dirough radical dissociation and recombination (equation 2). In fact, all four pathways have been experimentally observed with bis-7,7-(dimethyl)allyl ether (24 equation 8). Anions derived from allyl vinylcyclopropylmethyl ethers (e.g. i) rearrange by competing, 1,2, 1,4, homo-2,5, homo-4,5 and radical dissociation-recombination pathways. Nakai has shown that 1,4-rearrangement proceeds with retention of stereochemistry in the cyclohexenyl system (29 equation 9), as required by orbital symmetry considerations. ... 

As an example, treatment of allyl as-5-methyl-2-cyclohexenyl ether (5) with butyllithium in tetrahydrofuran at —85 JC affords the [2,3] Wittig product 6. which is then transformed to the oxy-Cope product 7 by reaction with potassium hydride in the presence of 18-crown-6. However, this two-step sequence is accompanied by the tandem process 5 -> 6 -> 7. since reaction of 5 gives a 62 14 mixture of 6 and 7. The overall transformation proceeds with exclusive cis selectivity1178. 

Claisen rearrangement of allyl vinyl ethers is catalyzed by palladium(II). Treatment of E-2-buten-l-yl 1-cyclohexenyl ether (R = CH3, = H) with 5% PdCl2(MeCN)2 at... 

Autoxidation, the oxidation of organic compounds by air, normally occurs via a radical chain mechanism. For example, cyclohexene undergoes allylic CH abstraction by an initiator, and the resulting cyclohexenyl radical reacts with O2 to give the corresponding hydroperoxy radical that abstracts an H from cyclohexene. In this case the final product is the allylic hydroperoxide. Conversion of ethers to the hydroperoxides is another familiar example. The conversion of cumene to phenol and acetone is a commercial application of the reaction (equation 9). 

Pd-C, 10% KOH, MeOH, rt, 8 h, 71-100% yield. Other allyl ethers such as prenyl, cinnamyl, cyclohexenyl and 2-methylpropenyl ethers are cleaved similarly. ... 

The cyclization of ort/zo-allyl phenols was reported by Murahashi in the late 1970s. The reaction of the 2-(2-cyclohexenyl)phenol (Equation 16.110) was one of the early examples of Wacker-type reactions with alcohol nucleophiles and has been re-investigated in more recent years with chiral catalysts. Intramolecular reactions of alkene-ols and alkenoic acids form cyclic ethers and lactones. These reactions were reported by Larock and by Annby, Andersson, and co-workers, and examples are shown in Equations 16.111 and 16.112. °° ° The use of DMSO as solvent was important to form the lactone products. More recently, reactions with alcohols were reported by Stoltz to form cyclic ethers by the use of pyridine and related ligands in toluene solvent. - The type of ligand, whether an additive or the solvent, is crucial to the development of these oxidative processes. However, the features of these ligands that lead to catalysis are not well understood at this time. 

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