Allyl sulfoxides

The allyl sulfoxide-allyl sulfenate rearrangement can be used to prepare allylic alcohols.275 The reaction is carried out in the presence of a reagent, such as phenylthi-olate or trimethyl phosphite, that reacts with the sulfenate to cleave the S—O bond. 

Allyl chloride is presumed to be metabolized to allyl alcohol, which could then be further metabolized via two pathways to form either acrolein or glycidol, from which a variety of metabolites could result. Metabolites identified in rat urine are 3-hydroxy-propylmercapturic acid and allyl mercapturic acid and its sulfoxide. Allyl glutathione and S-allyl-L-cysteine have been detected in the bile of dosed rats. In-vitro metabolism of allyl chloride results in haem destruction in microsomal cytochrome P450 (lARC, 1985). 

Adipic acid a-Alanine Allyl ethyl sulfoxide Allyl trichloroacetate... 

Allylic oxidation is carried out by addition of one equivalent of selenium dioxide. First Se02 will react with the alkene in a [4 + 2] cycloaddition reminiscent of the ene reaction. The initial product is an allylic selenic acid 40, which undergoes - like an allylic sulfoxide -allylic rearrangement to give an unstable intermediate, which decomposes rapidly to the allylic alcohol 42.16... 

The next example makes more involved use of these [2,3]-sigmatropic allylic sulfoxide-allylic alcohol rearrangements. It comes from the work of Evans (he of the chiral auxiliary) who, in the early 1970s, first demonstrated the synthetic utility of allylic sulfoxides. Here he is using this chemistry to make precursors of the prostaglandins, a family of compounds that modulate hormone activity within the body. 

The stereochemical features of the allyl sulfoxide-allyl sulfenate rearrangement involve the creation of a new double bond and the possibility of chirality transfer6 7. The stereochemical outcome can be predicted from the configuration of the starting material. 

Like allyl sulfoxides, allylic selenoxides rearrange via a highly ordered five-membered transition state. The arguments, already presented for the allyl sulfoxide rearrangement (Section 4.11.2.1.2.), apply for the rationalization of the high E selectivity of double-bond formation. Table 7 shows some examples7,8,12-15 for the strong preference for E double bonds (see also reference 2, Table V-2, p 148). Trisubstituted (A)-allyl alcohols are also obtained from allyl selenides with a substituent at C-2 of the allylic moiety (entries 8-10)7,8. 

Sulfoxides are optically active at the S atom. The natural ( + ) isomers are better substrates than the (—) isomers or the racemic mixture 18, 42). Among saturated alkyl groups, the garlic enzyme is most active on the ethyl derivative 18) while the onion enzyme prefers the propyl derivative (42). The rate differences (at substrate concentration = 0.02M) are caused solely by differences in 42). However, the natural alkenyl sulfoxides (allyl in garlic, 1-propenyl in onion) are the best substrates for the respective enzymes 18,43), and the onion enzyme... 

Allylic sulfoxides (181) and sulfenates (182) are related by a reversible reaction (equation 56). The equilibrium is shifted towards the sulfoxide. Due to the low barrier associated with this 2,3-shift optically active allylic sulfoxides can racemize at room temperature. Accordingly, the reaction of an alcohol (183) wift PhSCl via sulfenate (182) continues through the 2,3-rearrangement to the sulfoxide. Allylic sulfenates are very seldom isolable. When, conversely, an allylic sulfoxide (181) is heated in the presence of a thiophile (P(OMe)3, R NH, NaSR), the sulfenate (182) is removed from the equilibrium mixture by O—S bond cleavage. The ultimate reaction product obtained from an allylic sulfoxide, therefore, is an allylic alcohol (equation 56). 

M. Johnston, R. Raines, C. Walsh, and R. A. Firestone (1980), Mechanism-based enzyme inactivation using an allyl sulfoxide-allyl sulfenate ester rearrangement, J. Amer. Chem. Soc. 102,4241-4250. 

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