6-Membered P-Heterocycles: 1,2-Dihydro-, 1,2,3,6-Tetrahydro- and 1,2,3,4,5,6-Hexahydrophosphinine 1-Oxides

The members of a logically built P-heterocyclic family are discussed systematically to show a dynamically developing discipline of organophosphorus chemistry. Dichlorocyclopropanation of 2,5-dihydro-1H-phosphole oxides led to 3-phosphabicyclo[3.1.0]hexane 3-oxides that were useful intermediates for the synthesis of ring expanded products, such as 1,2-dihydrophosphinine oxides and 3-alkoxy-1,2,3,6-tetrahydrophosphinine oxides. Catalytic hydrogenation of 1,2-dihydrophosphinine oxides gave 1,2,3,4,5,6-hexahydrophosphinine oxides. Selective reduction of the α,β-doublebond of 1,2-dihydrophosphinine oxides via hydroboration led to 1,2,3,6-tetrahydrophosphinine oxides. Michael addition of >P(O)H species to the electron-poor double-bond of 1,2-dihydrophosphinine oxides afforded 1,2,3,6- tetrahydrophosphinine oxides with exocyclic P-function in position 3. Hydrogenation of these P-heterocycles led to the corresponding hexahydrophosphinine oxides. Stereostructure and conformation of the tetra- and hexahydrophosphinine oxides were elucidated by stereospecific NMR couplings and/or quantum chemical calculations. After deoxygenation, some of the above P-heterocycles were suitable P-ligands in transition metal complexes. The 1,2-dihydrophosphinine oxides were also useful in the synthesis of aromatic phosphinines, phosphepine derivatives and phosphabicyclo[2.2.2]octene oxides, as well as hetrocyclic β-oxophosphoranes.