Borane-tetrahydrofuran complex is a selective, electrophilic reducing agent. We report a simple and facile synthesis of tritiated borane-THF complex at high specific radioactivity. Li-3H, synthesized from carrier-free tritium gas and dispersed in dry tetrahydrofuran, was treated with boron trifluoride etherate to produce borane-THF complex (ca. 3060 GBq/mmol). (The maximum theoretical specific radioactivity of tritium is 1063 GBq/milliatom = 28.76 Ci/milliatom.) This complex was used in an exemplary reduction of 2-naphthoic acid to 2-naphthalenemethanol, in high yield. Both the borane-THF complex and the reduction product were characterized by a combination of , 3 *H, and UB NMR techniques, as appropriate. The reduction product was found to have >94% of the maximum theoretical specific radioactivity, and all of the tritium at the reduced position.

SummarySimple and facile syntheses of highly deuterated and tritiated LiBH4, NaBH4 and KBH4 were achieved by hydrogen isotope exchange with deuterium or tritium gas at elevated temperatures. The exchange products were characterized by boron, proton and deuterium or tritium NMR spectroscopy. The extent of isotope (2H or 3H) incorporation was calculated from the patterns of *lB NMR spectra. Several samples of tritiated NaBH4 were treated with BF3-Et20 to produce tritiated borane-THF complex, which is an electrophilic reducing agent. The utility of both the borohydride reagents and borane-THF complex in labelling reactions was confirmed by exemplary reductions leading to specifically labelled products. The extent and orientation of labelling in the reduction products was assessed by a combination of radio-HPLC analysis, 1H, *H or 3H NMR and mass spectrometry.

SUMMARYNaB'H, and LiB'H, at 78% and 97% isotopic enrichments, respectively, were used in the synthesis of 'H-labeled 1-(6-chloro-3-pyridyl)-methyl-2-nitromethyleneimidazolidine (CH-IMI) and N'-[(6-chloro-3-pyridyl) methyl1 -N"-cyano-N' -methylacetamidine (acetarniprid) (two very potent insecticides) and of 1-(6-chloro-3-pyridyl)methyl-2-iminoimidazolidine (desnitro-IMI) (a metabolite of the commercial insecticide imidacloprid) . 6-Chloronicotinoyl chloride was treated with either NaB'H, in methanol or LiE3H, in tetrahydrofuran and the resulting alcohol transformed to 2-chloro-5-chloromethylpyridine, which was then coupled to N-cyano-"-methylacetamidine to give ['HI acetamiprid (45 Ci/mmol) . 2-Chloro-5-chloro [3Hlmethylpyridine was also reacted with ethylenediamine and the product was either refluxed in absolute ethanol with 1,l-bis (methylthio) -2-nitroethylene to provide ['HICH-IMI or reacted in toluene with a solution of cyanogen bromide to produce ['Hldesnitro-IMI (each 5 5 Ci/mmol).

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NaB3H4 and LiB3H4 at 78% and 97% isotopic enrichments, respectively, were used in the synthesis of 3H‐labeled 1‐(6‐chloro‐3‐pyridyl)‐methyl‐2‐nitromethyleneimidazolidine (CH‐IMI) and N′‐[(6‐chloro‐3‐pyridyl)methyl]‐N″‐cyano‐N′‐methylacetamidine (acetamiprid) (two very potent insecticides) and of 1‐(6‐chloro‐3‐pyridyl)methyl‐2‐iminoimidazolidine (desnitro‐IMI) (a metabolite of the commercial insecticide imidacloprid). 6‐Chloronicotinoyl chloride was treated with either NaB3H4 in methanol or LiB3H4 in tetrahydrofuran and the resulting alcohol transformed to 2‐chloro‐5‐chloromethylpyridine, which was then coupled to N‐cyano‐N′‐methylacetamidine to give [3H]acetamiprid (45 Ci/mmol). 2‐Chloro‐5‐chloro[3H]methylpyridine was also reacted with ethylenediamine and the product was either refluxed in absolute ethanol with 1,1‐bis(methylthio)‐2‐nitro‐ethylene to provide [3H]CH‐IMI or reacted in toluene with a solution of cyanogen bromide to produce [3H]desnitro‐IMI (each 55 Ci/mmol).