Hydrolytic cyclohexene

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

Alkenes react with xenon difluoride and diphenyldiselcnide to give the corresponding products of 1,2-fluoroselenation. Formation of phcnylselenyl fluoride as the unstable intermediate has been postulated. Cyclohexene (9) has been treated with xenon difluoride and diphcnyl-diselenide in dichloromethane at — 20 C to form tran.v-l-fluoro-2-phenylselenocyclohexane (10) in 73% yield. 2-Phenylselcnocyclohexanol (11) is the major byproduct in 5% yield due to the hydrolytic instability of the fluoroselenide 10. 

MeN HSO4) [145] (Table 1.6). This catalyst system was attractive because it could be used to epoxidize imreactive terminal alkenes with H2O2, and because it could operate without chlorinated solvents, which can be toxic and carcinogenic. A drawback was that the system was not effective in the epoxidation of styrene, because of hydrolytic decomposition of the epoxide, and of cyclohexene, because of the production of adipic acid [146]. 

Dihydro-2-isopropyl-3.6-dimethoxypyrazine, a bis(lactim)ether, is converted into the 5-di-azo compound 1 by lithiation and diazo group transfer. The intermediate diazo compound reacts at room temperature with olefins such as cyclohexene to produce the cyclopropane derivatives with excellent diastereoselectivity . The derivative from cyclohexene is hydrolyzed by acid treatment to give methyl 7-cv(cfo-aminobicyclo[4.1.0]hcptane-7-carboxylate. The bis(lac-tim)ether diazo compound 1 is also involved in an exceptional asymmetric [2 + 1J cycloaddition producing cnantiomerically pure cyclopropenc derivatives4. Thus, reactions of the diazo compound with monosubstituted alkynes afford the spiro compounds as one diastereomer. Hydrolytic removal of the auxiliary and protection of the amino group provides enantiomerically pure methyl l-amino-2-arylcyclopropene-l-carboxylates in moderate overall yield. 

The synthetic applications of benzothiazoles appeared to be limited by the fact that the thiazole ring cannot be hydrolytically cleaved. However, this problem was solved by quatemization followed by reduction with NaBH4 to produce 3-methyl-2,3-dihydrobenzothiazole, as shown in the synthesis of cyclohexene-1-carbaldehyde [104] ... 

Characterization of the by-products derived from HMPA has proved to be very difficult due to their high dilution in the reaction mixture, their high soiubility in water, and to simultaneous photodecomposition of HMPA. Photolysis of HMPA produces hydrogen or a mixture of Hj, HD, and Dj if small amounts of DjO are introduced in the reaction mixture. The only product derived from HMPA which could be completely characterized indicated that a hydrolytic process was involved. " The lowering of chemical yields observed when double bonds are present in the starting material and for reactions occurring in the presence of cyclohexene indicate that coupling products between the HMPA radical and the substrate or cyclohexene have been formed (Scheme 8). ... 

Synthetic applications of benzothiazoles appear to be limited due to their hydrolytic stability. However, as shown in the following synthesis of cyclohexene-1-carbaldehyde (22) [368], the benzothiazole system can be modified by quaternization and reduction to a 2,3-dihydrobenzothiazole system 21, which (as aldehyde thioaminal) is acid-labile and thus can be readily cleaved by hydrolysis to the corresponding aldehyde 22. 

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