Benzaldehyde Clemmensen reduction

In the case of aryl aldehydes and ketones, benzaldehyde afforded benzyl alcohol as the major product, but acetophenone and its para-substituted derivatives carrying such groups as OMe, Cl or OH provided ethylbenzene derivatives in good yields. As with Clemmensen reduction, the alcohol produced in this reduction cannot be further reduced, and the alcohol is not therefore an intermediate. Still uncertain in the reaction mechanism of electrolytic reduction, however, is the role of adsorbed hydrogen. ... 

Arylcarbenes are formed from benzaldehyde and some of its derivatives if the Clemmensen reduction is performed using boron trifluoride or another Lewis acid instead of hydrochloric acid. If the reaction is carried out in the presence of an alkene, which is often used as solvent, addition to the C-C double bond takes place and cyclopropane formation results in low to fair yields. The arylcyclopropanes are always formed as mixtures of stereoisomers and, in all cases but two, the endo-isomcr is significantly predominant. Thus, when a mixture of 4-methoxybenzaldehyde, boron trifluoride-diethyl ether complex and a considerable excess of cyclohexene was allowed to react with amalgamated zinc, 7-(4-methoxyphenyl)bicy-clo[4.1.0]heptane (1) was obtained in 60% yield. 

---