Reduction of various bonds involving heteroatoms

Alkali metal amides cannot generally be prepared by direct reduction of the N-H bond. An exception is the rapid attack of potassium by 1,3-propanediamine, but catalytic amounts of ferric nitrate are necessary.i47 resulting strong base. 

KAPA (Eq. 29), isomerizes disubstituted alkynes to the terminal position. NAPA, the sodium analogue, is prepared without the iron salt and behaves similarly. 

Other heteroatomic bond cleavages have found synthetic applications. One of these is the reduction of diphenyldiselenide by sodium under irradiation at 50 kHz, giving sodium phenylselenide (Eq. 30, see p. 371).1 8 

The appropriate solvent is xylene, but its high boiling point makes it impractical for many applications. The slow reaction in THE is greatly accelerated by catalytic amounts of benzophenone. The sonochemically prepared reagent exhibits enhanced nucleophilic properties, used in the synthesis of the ionophore antibiotic M 139603. For example, no side product is formed in the reaction with methyl p-iodopropionate (Eq. 31). The reason for this higher reactivity remains obscure. 

The cleavage by lithium of a P-C bond in tertiary phosphines gives the phosphide anion. The reduction is accelerated by a factor of 10 imder sonication, and gram quantities of substrates undergo the reaction successfully in a cleaning bath. From methyl diphenyl phosphine, the reaction is selective and only a P-aryl bond is cleaved. The sonication time increases with the amount of substrate. This reaction would probably be improved with the use of probe generators. 

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