Enantiomerically Pure N Chirally Substituted 1,3-Benzazaphospholes: Synthesis, Reactivity toward tBuLi, and Conversion to Functionalized Benzazaphospholes and Catalytically Useful Dihydrobenzazaphospholes

Catalytic C–P coupling of chiral o-bromoanilines 1a–c to the corresponding o-phosphonoanilines 2a–c, reduction to the phosphines 3a–c, and final acid-catalyzed cyclocondensation represents a convenient access to the title compounds 4a–c. Reaction of 4a,b with tBuLi allows solvent-dependent directed lithiation leading either to 2-lithiobenz­azaphospholes with a −PCLi–NR– substructure (in Et2O/KOtBu), in the case of anisyl substitution accompanied by partial additional lithiation in o-position of the MeO-group, or to regiospecific “normal” addition with formation of −P­(tBu)–CHLi–NR– species. These were trapped by ClSiMe3, CO2, or MeOH to give the corresponding substitution products 7b, 8b, 10b, 11a,b and 12a,b, respectively. 12a,b, containing the P–C–COOH structural unit, forms with Ni­(COD)2 in THF very efficient ethylene oligomerization catalysts with high selectivity for linear α-olefins. The structure elucidation of the products is based on conclusive solution NMR data and crystal structure analyses of the 1-(1S)-anisylethyl compounds 3b and 4b.