Several organometallic reagents such as lithium 2lithio 4-methylphenolate 1 intermediates formed by orthometallation of o-bromoaryloxy-phosphorus(V)-2 or -phosphorus(III)-derivatives 3 with magnesium and sodium, respectively, as well as O-methoxymethylprotected o-lithio-4-methylphenol 4 were used to synthesize suitable precursors 5,6,9,10 of primary and secondary o-phosphinophenols. The P-C bond formation involved coupling with ClPR(NMe 2 ), CIPR(O)(OEt) or an intramolecular carbanionic O β C shift of the P-substituent. Reduction with LiAlH 4 , in the cases of phosphonous or phosphinous acid amides after alcoholysis (to 7,8,11), produced primary and secondary o-phosphinophenols 12, respectively, or Oprotected derivatives 13. o-Phosphinophenols 12 are easily protonated at the phosphorus atom, supported by a P β«Χβ¬ -H. . .O hydrogen bridge. Metallation (14), acylation, and silylation (16, take place preferably at the hyxdroxy group and alkylation at the phosphorus atom. Alkylation of 12 and 14 was found to be slow, but C,O-dilithiated species 15 react to give P-secondary (12b,d,e,) or P-tertiary products (20,21). Cyclization of 15a with Me 2 SiCl 2 affords the 2,3-dihydro-1,3,2benzoxaphosphasilol 22, cyclocondensation of 12c with RP(NMe 2 ) 2 or ClP(NMe 2 ) 2 furnishes 2,3-dihydro-Dedicated to Prof. William E. McEwen on the occasion of his seventy-fifth birthday.