Ruthenium acid diester

Fig. 17.29. The Ru04 cleavage of a phenyl ring is exemplified by the case of an altylated aromatic compound using the modified Lemieux-von Rudloff conditions (Figure 17.26). The reaction involves three key intermediates the cr-ketoalde-hyde A, the a-keto acid E, and the ruthenium(VIII) acid diester G. It is unclear how the reaction of E —> G proceeds. In the last step, G undergoes a fragmentation via a cyclic transition state and forms a substituted acetic acid I, Ru03 and carbon dioxide.

Chiral phosphonous acid diester induces the kinetic resolution of racemic a-substituted y-unsaturated carboxylic acids through asymmetric protolac-tonization (Scheme 53) (130L2838). Dinamic kinetic resolution with Candida antartica lipase B and the ruthenium catalyst [RuCl(CO)2(T -C5Ph5)] of several homoallylic alcohols is applied in the key step to the synthesis of enantiomericaUy pure 5,6-dihydro-2ff-pyran-2-ones ( [13CEJ13859]). 

Ruthenium tetroxide is a four-electron oxidant which directly transforms alkenic compounds into oxidative cleavage products, i.e. carbonyl compounds and carboxylic acids.288 The reaction can be visualized as proceeding according to a [4 + 2] cycloaddition of the cis-dioxo moiety with the alkene, resulting in the formation of a RuVI cyclic diester which decomposes to ruthenium(IV) dioxide and oxidative cleavage products (equation 114).288 This reaction can be made catalytic... 

Oxidation of the iV-alkoxycarbonyl-2-azabicyclo[2.2.0]hex-5-ene 158 with ruthenium tetroxide followed by esterification with diazomethane affords the cis-2,3-diester of azetidine 159 (R = Me) in 67% overall yield. The N-protecting group can be easily removed from the diacid by acidic hydrolysis to give acidic amino acid 160 in 85% yield. Strangely, the 2,3-diester 159 (R = Me) upon acidic hydrolysis failed to give any of the amino acid. This approach to azetidines is useful because 158 is readily available from pyridine in three steps <2003CPB96>. 

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