Enantiomerically Pure Phosphaalkene-Oxazolines (PhAk-Ox): Synthesis, Scope and Copolymerization with Styrene

The design of a synthetic route to a class of enantiomerically pure phosphaalkeneoxazolines (PhAk-Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha-Peterson reaction) was used as the P?C bond-forming step. Attempted condensation of PhC(?O)Ox (Ox=CNOCH(iPr)CH2) and MesP(SiMe3)Li gave the unusual heterocycle (MesP)2C(Ph)?CN-(S)-CH(iPr)CH2O (3). However, PhAk-Ox (S,E)-MesP?C(Ph)CMe2Ox (1?a) was successfully prepared by treating MesP(SiMe3)Li with PhC(?O)CMe2Ox (52?%). To demonstrate the modularity and tunability of the phospha-Peterson synthesis several other phosphaalkeneoxazolines were prepared in an analogous manner to 1?a: TripP?C(Ph)CMe2Ox (1?b; Trip=2,4,6-triisopropylphenyl), 2-iPrC6H4P?C(Ph)CMe2Ox (1?c), 2-tBuC6H4P?C(Ph)CMe2Ox (1?d), MesP?C(4-MeOC6H4)CMe2Ox (1?e), MesP?C(Ph)C(CH2)4Ox (1?f), and MesP?C(3,5-(CF3)2C6H3)C(CH2)4Ox (1?g). To evaluate the PhAk-Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1?a and styrene were subjected to radical-initiated copolymerization conditions to afford [{MesPC(Ph)(CMe2Ox)}x{CH2CHPh}y]n (9?a: x=0.13n, y=0.87n; GPC: Mw=7400 g?mol-1, PDI=1.15).