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

Abstract

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 t...