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Phosphine oxides bearing two or three 2-pyridyl groups were found to react with organometallic compounds affording 2,2′-bipyridyl, 2-substituted pyridines and pyridine in substantial yields. Both ligand exchange and ligand coupling appear to take place within the penta-coordinated phosphorus intermediates formed incipiently.

Characteristic properties of organosulfur compounds bearing azaheteroaromatics and their applications for organic synthesis are described as follows : 1) strategies for development of new synthetic procedures by using thione-thiol tautomerisms of pyridyl derivatives. 2) studies on new ligand coupling reactions of benzyl pyridyl and related sulfoxides with Grignard reagents and butyl lithium together with their stereochemistry and mechanisms. 3) preparation and reactions of pyridyl and quinolyl Grignard reagents. 4) ipso-substitution reactions on the azaaromatic compounds bearing sulfinyl and sulfonyl groups with nucleophiles.

The reaction of p-benzenesulfonylphenyl crotyl sulfoxide with Grignard reagents is considered to proceed via formation of an incipient σ-sulfurane to afford the coupling product, p-benzenesulfonyl-crotylbenzene, in which the geometric configuration of crotyl group was completely preserved. No rearrangement was observed in the coupling reaction of p-benzenesulfonylphenyl α-methylallyl sulfoxide. Such a complete retention of geometric configuration was also found in the reactions of 2-pyridyl and p-benzenesulfonylphenyl styryl sulfoxides with Grignard reagents.

The reaction between methyl 2-pyridyl sulfoxide (1) with Grignard reagents afforded 2,2′-bipyridine (2) in moderate yield. The reaction is considered to involve initial ligand exchange to generate 2-pyridylmagnesium halide which in the subsequent step attacks the original sulfoxide to form the σ-sulfurane that undergoes ligand coupling to afford 2. The reaction of t-butyl 2-pyridyl sulfoxide (3) with C6H5MgBr, however, gave only 2-phenylpyridine (4). This may be due to steric hindrance to the initial ligand exchange. Formation of 2 is a convenient process for preparation of 2,2′-bipyridines bearing various substituents.

The reaction of 2-pyridyl sulfoxides such as (I) with a Grignard reagent is found to give the ligand-coupling product such as (II) in excellent yield.

The reaction of N-(4-tosyl)sulfilimines with lithium aluminum hydride was found to proceed via the ligand-coupling within the σ-sulfurane formed as an intermediate by giving the corresponding sulfides in excellent yields under mild conditions.