Epoxides, vinyl activated

Thiiranes (77) show some juvenile hormone activity, but the epoxide is often more active. Thiophosphates of 2-mercaptomethylthiirane are strong contact insecticides 2-chloromethylthiirane and4-vinyl- 1,2-epithiocyclohexane are nematocides. Severalthiirane 1 -oxides are reported to be insecticides, molluscicides and herbicides (68USP3413306). 1,2-Epithio-1,2,3,4-tetrahydronaphthalene is a mild herbicide. 

While generation of a Mn(V)oxo salen intermediate 8 as the active chiral oxidant is widely accepted, how the subsequent C-C bond forming events occur is the subject of some debate. The observation of frans-epoxide products from cw-olefins, as well as the observation that conjugated olefins work best support a stepwise intermediate in which a conjugated radical or cation intermediate is generated. The radical intermediate 9 is most favored based on better Hammett correlations obtained with o vs. o . " In addition, it was recently demonstrated that ring opening of vinyl cyclopropane substrates produced products that can only be derived from radical intermediates and not cationic intermediates. ... 

A retrosynthetic analysis of fragment 152 can be completed through cleavage of the C16-C17 bond in enone 155, the projected precursor of epoxide 152. This retrosynthetic maneuver furnishes intermediates 156 and 157 as potential building blocks. In the forward sense, acylation of a vinyl metal species derived from 156 with Weinreb amide 157 could accomplish the construction of enone 155. Iodide 153, on the other hand, can be traced retrosynthetically to the commercially available, optically active building block methyl (S)-(+)-3-hydroxy-2-methyIpropionate (154). 

For the construction of the I ring, the vinylic group introduced to activate the y-hydroxy epoxide moiety of 28 towards cyclization is an acrylic ester residue, which concomitantly allows cyclization on the allylic position, with formation of the tricyclic compound 29 containing the IJK fragment of the natural product, and fur-... 

Increasing use is being made of pyran syntheses based upon [4 + 2] cycloadditions of carbonyl compounds. The appropriate unsaturated aldehyde with ethyl vinyl ether yields 53 with peracids this affords an epoxide that undergoes ring contraction to the aldehyde 54 (Scheme 23) and rhodium catalyzed decarbonylation affords the required 3-alkylfuran with the optical center intact.116 Acetoxybutadiene derivatives add active carbonyl compounds giving pyrans that contract under the influence of acids to give... 

Konishi et al.97 synthesized porphyrin compound 127. As shown in Scheme 4-44, asymmetric epoxidation of prochiral olefins such as styrene derivatives and vinyl naphthalene by iodosobenzene has been achieved by using this porphyrin complex as the catalyst in the presence of imidazole. The optically active epoxides were obtained with moderate ee. 

In male and female rats exposed to 10, 50, 250, or 12 50 ppm vinyl bromide in a lifetime inhalation study, there was a dose-related increase in angiosarcomas of the liver in both sexes. A significant increase in hepatocellular neoplasms was also seen in male rats exposed at 250ppm and in female rats exposed at 10, 50, and 250ppm. The lack of increase in hepatocellular neoplasms in rats at the 12 50 ppm level was probably due to their early mortality and termination at 72 weeks. In limited mice studies, no local tumors were produced by skin application or subcutaneous administration. Vinyl bromide is mutagenic in bacterial assays and Drosophilas It is activated via a P-450-dependent pathway to its epoxide that can covalently bind to DNA. ... 

Carbohydrates as well as proteins are effectively coupled to divinyl-sulfone-activated agaroses. This variant is often more favorable then the activation by epoxides. As further advantage, the resulting vinyl group serves as a spacer. 

There is also an enzyme for removal of methyl and ethyl groups from bases by oxidizing them to their respective aldehydes-the Aik B repair enzyme. Lipid epoxides, which may be produced in inflammatory tissue and can yield alkylated bases, will also be repaired by this enzyme (Fig. 6.47). Metabolic activation of vinyl chloride will also yield the same adduct (see chap. 7). 

Vinyl chloride is a chemical used in the manufacture of plastics, which is carcinogenic and causes various toxic effects, including liver injury and damage to the bones and skin. Liver hemangiosarcomas are produced in animals and humans. Vinyl chloride undergoes metabolic activation by cytochrome P-450 to an epoxide, which may interact with DNA and form adducts (ethenodeoxyadenosine and ethenodeoxycytidine), which leads to mutations. These can be detected in white cells, and a mutant p21 ras protein can be detected in the serum of exposed workers. Also, reaction with GSH occurs. 

Rosenkranz, H.S. Poirier, L.A. (1979) Evaluation of the mutagenicity and DNA-modifying activity of carcinogens and noncarcinogens in microbial systems. J. natl Cancer Inst., 62, 873-892 Ross, A.M., Pohl, T.M., Piazza K., Thomas, M., Fox, B. Whalen, D.L. (1982) Vinyl epoxide... 

This oxidation is unique, since only silver is capable of epoxidizing ethylene, and silver is active only in the oxidation of ethylene. A low-surface-area a-alumina is usually applied to support about 10-15% silver. Organic halides (1,2-dichloro-ethane, ethyl and vinyl chloride) are added as moderators, and additives (Cs, Ba) are also used to increase selectivity. At present selectivity in industrial oxidations is about 80%. 

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