Phenyl ring, ozonolysis

The catalytic properties of Co in the hydrocarbon oxidation have been the subject of intensive investigations [107], It has been established that during the cumene-AcOH ozonolysis in 1 1 (v v) in the presence of Co(AcO)2 the oxidation reaction is accelerated (Fig. 17).In contrast to the noncatalysed process in the catalyzed by transition metal salts the ozonolysis is characterized by 1) absence of ozonides formation that is indicative of the absence of ozone interaction with the phenyl ring and 2) the main product is DMPC, the accumulation rate of which proportional to the concentration of Co after the 10 min. The initial rates of CHP formation do not vary with the changes in Co + but after the 15 min the rates increase with [Co ]. It can be seen from Table 9 that if we assume the ozonolysis of pure cumene as a reference then the addition of AcOH results in autoretardation of the oxidation rate and to reduction of the products yield. The ratio [IP]/[03 reaches value of 6.9. 

An achiral ketone (S OS) was used to prepare protected alcohol 5.206 via condensation with S-phenethylamine, and that protecting group was also an auxiliary Removal of the benzylic group and re-protection with Boc allowed Birch reduction s of the aromatic ring to give 5.207. Ozonolysis in methanol led to methyl 4-(N-Boc amino)-6-methyl-3-oxoheptanoate, 5208. In this synthesis, the phenyl ring functioned as the carboxyl surrogate and asymmetric induction in 5.208 arose from the chiral auxiliary introduced earlier in the sequence. 

Co-ozonolysis of /< r/-butylethene (3,3-dimethyl-l-butene) in the presence of benzoyl cyanide gave as major product (55%) 3-cyano-3-phenyl-l,2,4-trioxolane 103 along with 13% of the ft /t-butyl-substituted 1,2,4-trioxolanes 108 as a mixture of stereoisomers in 53 47 Z/E ratio which could be assigned from nuclear Overhauser effect (NOE) data, as only the (Z) compound shows an NOE enhancement (across the 1,2,4-trioxolane ring) of the ortho-phenyl protons upon irradiation of the Bu methyl groups (Equation (10) and Figure 5). 

Another of the arylalanines, L-tryptophan, was used at the same laboratories [81] for the synthesis of novel benzazepines (56) as dual inhibitors of ACE and thromboxane synthase (Scheme 5.25). Ozonolysis of 7V-acetyl l-tryptophan to effect scission of the indole ring followed by 7V-protection gave the 4-keto acid (57) as a cyclization precursor. Downstream transformations included diastereoselective reduction of the ketone functionality and reductive alkylation of the amine substituent with ethyl 2-oxo-4-phenyl-butanoate. 

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