Oxidative cleavage rearrangement

This excellent method of oxidative cleavage (/) of carbon-silicon bonds requires that the silane carry an electronegative substituent (2), such as alkoxy or fluoro. Either hydrogen peroxide or mcpba may be used as oxidant, and the alcohol is produced with retention of configuration (3). Fluoride ion is normally a mandatory additive in what is believed to be a fluoride ion-assisted rearrangement of a silyl peroxide, as shown below ... 

As described in the preceding paragraphs, oxidation products of carotenoids can be formed in vitro as a result of their antioxidant or prooxidant actions or after their autoxidation by molecular oxygen. They can also be found in nature, possibly as metabolites of carotenoids. Frequently encountered products are the monoepoxide in 5,6- or 5, 6 -positions and the diepoxide in 5,6 5, 6 positions or rearrangement products creating furanoid cycles in the 5,8 or 5, 8 positions and 5,8 5, 8 positions, respectively. Products like apo-carotenals and apo-carotenones issued from oxidative cleavages are also common oxidation products of carotenoids also found in nature. When the fission occurs on a cyclic bond, the C-40 carbon skeleton is retained and the products are called seco-carotenoids. 

Wipf and coworkers used a Claisen rearrangement of allyl phenyl ethers 4-309 followed by an enantioselective carboalumination using the chiral Zr-complex 4-310 and trimethyl aluminum (Scheme 4.67) [104]. After an oxidative work-up of the intermediate trialkylalane, the corresponding alcohols 4-311 were obtained with up to 80% ee and 78% yield. One can also transfer an ethyl group using triethyl aluminum with even better ee-values (up to 92%), but the yields were rather low (42%) due to a more sluggish oxidative cleavage of the Al-C bond. 

The one-electron oxidation of iV-benzylphenothiazine by nitric acid occurs in the presence of /i-cyclodextrin, which stabilizes the radical cation by incorporation into its cavity. The reaction is inhibited by adamantane, which preferentially occupies the cavity. Novel Pummerer-type rearrangements of / -sulfinylphenyl derivatives, yielding /7-quinones and protected dihydroquinones, and highly enantioselective Pummerer-type rearrangements of chiral, non-racemic sulfoxides have been reviewed. A comprehensive study has demonstrated that the redox potential for 7- and 8-substituted flavins is linearly correlated with Hammett a values. DFT calculations in [3.3.n]pro-pellanes highlight low ionization potentials that favour SET oxidative cleavage of the strained central C-C bond rather than direct C-H or C-C bond attack. Oxidations and reductions in water have been reviewed. ... 

While secondary alcohols are now relatively easy to prepare in enantiomerically-pure form, secondary amines have been more challenging. Larry Overman of UC Irvine reports (J. Am. Chem. Soc. 125 12412, 2003) the catalytic rearrangement of primary allylic alcohols such as 4 to the corresponding protected vinyl amine 5 with excellent . Hydrolysis of the amine 5 gives the GABA aminotransaminase inhibitor 6. Unnatural amino acids can be prepared by oxidative cleavage of the protected vinyl amines. 

In the first step 61 is dehydrocyclized to 67. This intermediate rearranges to 68, that yields 66 by nitrogen elimination. Further oxidation dehydrogenates 67 to 69, which decomposes to 63 and 64. Benzil (65) is produced by hydrolysis, 59 by oxidative cleavage of 61. 

Dufraisse announced that 138 was formed when an alkaline solution of hydroxyindanone 185 is treated with air or oxygen up to 80% 138 could be obtained in this way. This observation can be explained either by oxidation of an enolate ion to an oxiranol, with subsequent rearrangement, or by oxidative cleavage of the enolate ion to a benzilic acid (186), which after ring closure will lose CO2 and HjO to give 138 (Scheme 8). Compound 138 is also formed when n-benzoylbenzil (187) is treated with potassium hydroxide in ethanol a benzilic acid rearrangement may be the first step of the sequence. 

Oxidative cleavage of the organic fragment from the metal is possible using Ce and gives the tricyclic rearrangement product (34) in very high yields (equation 15) 45,46 The tetranitrile, (34), prepared in this manner has been used as a key intermediate in the synthesis of chiral 2-substituted triquinacene derivatives.51... 

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