Carbon-phosphorus bond formation: new methodologies for the preparation of organophosphorus compounds of biological interest

Abstract

The work presented in this dissertation deals with the development of new methodologies for P-C bond formation as well as synthesizing biologically relevant organophosphorus compounds. A distinct emphasis is given to the important synthetic targets, the H-phosphinates. A review of relevant literature is provided in Chapter 1. Chapter 2 describes the synthesis and structural analyses, of triphenylmethyl-containing phosphorus compounds. For the first time, both phosphonothioic and boranophosphonic acids have been characterized by single X-ray diffractometry. The third chapter details the preparation and the reactivity of phosphine-borane complexes.^Novel dialkoxyphosphine-borane complexes were introduced, both as general synthetic intermediates for the preparation of H-phosphinates or disubstituted phosphinic acids, and as boranophosphonate precursors.^Related to this chemistry, silylation of an H-phosphinate intermediate can also be conducted and the resulting phosphonite protected with borane. This allows the temporary protection of the sensitive P-H group, so that manipulations of the alkyl chain might be conducted. In chapter 4, the palladium-catalyzed cross-coupling reaction of dialkylphosphites with aryl and heteroaryl halides is presented. An efficient, versatile and economically attractive alternative to the original Hirao cross-coupling by using only 1 mol% (or less) Pd(OAc)2/dppf is described. Moreover, first example of palladium-catalyzed P-C bond formation between activated aryl chlorides and a phosphite are herein reported.^Chapter 5 focuses on the free-radical hydrophosphinylation of alkynes.^The triethylborane-initiated radical addition of sodium hypophosphite to terminal alkyne affords the previously unknown 1,1-bis-H-phosphinates, precursors of the biologically relevant 1,1-bisphosphonates (e.g., treatment of bone diseases). Thus, the oxidative conversion of 1,1-bis-H-phosphinates to the corresponding bisphosphonates, as well as the synthesis of a series of bio-conjugates (steroids, carbohydrates, fluoroquinolones) was investigated. In the last chapter, the palladium-catalyzed hydrophosphinylation of hypophosphorous acid derivatives to terminal alkynes is reported. In an effort to improve the regioselectivity of the reaction, various terminal alkynes were tested, as well as the solvent and catalyst system.