The reaction of various organosiliconhydrides including hydropolysilanes with methyl diazoacetate in the preence of copper catalyst gave α-silyl- and polysilyl- esters in 44 – 90% yields. The relative reactivities of a series of m- and p-substituted phenyldimethylsilane towards the active species generatedfrom the diazoacetate correlate well with the Hammett σ constants for the ring substituents,