Synthesis of 3-Phenyl Benzyl Alcohols

One of the more recent results of pyrethroid research in the late 1970 s/early 1 80 s consists of biphenyl-3-methylesters of certain pyrethroid acids, having an additionally strong activity against mites (Bifenthrin). Although the unsubstituted biphenylmethyl esters are of an appreciable activity [659, 660], the higher substituted ones are more interesting, particularly if the phenyl substituent is sterically forced out of plane. For synthesis, the classical methods of biphenyl chemistry had to be optimized to quite an extent (Reaction scheme 215). 

It usually comprises a radical reaction with a tendency to form the notorious side-products. Instead of the formerly common decomposition of a N-nitroso acetanilide 304 in benzene [661], the decomposition of diazonium salts [662, 663] is now preferred, optimally in the presence of orthoformic ester, which ensures a high 

Longer reaction sequences for the 4-phenyl-2-indanols start from biphenyl-2-methanol [668]. 

Hydroboranation of substituted indene gives the 3-indanol [666, 669]. Asymmetric induction with optically active pinene results in a larger enantiomeric excess of the more interesting enantiomer [670]. 

Another route to the biphenyl-2-methylmethanol for the commercial product needs a twofold Grignard reaction [641] (Reaction scheme 216) and yields the desired bifenthrin-alcohol 306 in 60% yield in four steps  

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