SYNTHESIS OF DIETHYL 1-[(C-13)METHYL]-3-PHENYL(1,3-C-13(2)BICYCLO[1.1.0]-BUTANE-EXO,EXO-2,4-DICARBOXYLATE

The synthesis of the triply 13C labeled molecule, diethyl 1‐[(13C)methyl]‐3‐Phenyl(1,3‐13C2)bicyclo[1.1.0]butane‐exo,exo‐2,4‐dicarboxylate is described. The unique feature of the synthesis is that in three instances we employed 13CO2 (from Ba13CO3) without using a high vacuum line. We found that excellent yields were obtained in two Grignard reagent carbonations and in a CO2 reduction using a mechanical pump which produced a vacuum of 0.05 torr. The synthetic sequence involved carbonation of phenylmagnesium bromide to give (α‐13C)benzoic acid, reduction with LiAlH4, conversion to the corresponding benzyl chloride followed by preparation of the Grignard reagent and carbonation to produce phenyl (1,2,‐13C2)acetic acid. Reaction with 13CH3Li provided 1‐Phenyl‐2‐(1,2,3‐13C3)‐propanone which, after conversion to its hydrazone and reaction with mercurous trifluoroacetate, yielded 1‐phenyl‐1‐(1,2,3‐13C3)propyne. Reaction twice with carboethoxycarbene (from ethyl diazoacetate) gave the desired triply 13C labeled bicyclobutane. Copyright © 1979 John Wiley & Sons, Ltd.