Geminal dimethyl moiety

The importance of the oxidation of the geminal dimethyl moieties appears to disappear in some of the later studies with pyrethroids. The reason for this may be difficulties in obtaining appropriate synthesized standards and setting up good chromatographic procedures for identifying such compounds in urine. The alternative explanation is that hydroxylation of the methyl group does not occur to any extent in the other pyrethroids. 

SCHEME 16 Transfonnation of enone 69 to geminal dimethyl moiety. 

Alkylidenemalonates were found to be excellent acceptor molecules (111). Reactions of lithium ylides with dimethyl alkylidenemalonates at —78 °C in THF in the presence of f-BuOH were diastereoselective for all the substituents R except methyl, producing Michael adducts as single diastereomers (Scheme 11.24). The only exception was dimethyl ethylidenemalonate, which produces an 86 14 mixture of diastereomeric adducts, the minor diastereomer being syn-adduct. Since dimethyl alkylidenemalonates bear two geminal methoxycarbonyl moieties, one is cis to the terminal substituent R and the other trans, so of these ester substituents can participate in chelate formation in the transition state. When the terminal substituent R is small, there is a chance for the syn-adduct to be produced, which... 

The alcohol moiety of (IR-frans)- and (lR-c T)-phenothrin is rapidly metabolized and eliminated, with the major excreted metabolite being either free or conjugated 4-OH PB acid (CAS no. 35065-12-4) (Miyamoto et al. 1974 Miyamoto 1976). Intact esters of (IR, cis) phenothrin were excreted in feces, one being 4-OH phenothrin (CAS no. NA), another carboxy phenothrin (CAS no. 79897-38-4) and carboxy 4 -OH phenothrin (CAS no. 79861-56-6). Oxidation of one of the geminal dimethyl groups has also been reported (Miyamoto 1976). According to Elliott et al. (1976), phenothrin is metabolized like permethrin except for alterations on the isobutenyl group not seen for the dichlorovinyl side chain of permethrin. 

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