Hexahydrophosphinine oxides

Keywords 1,2-Dihydrophosphinine oxide, 1,2,3,4,5,6-Hexahydrophosphinine oxide, P-Oxophosphoranes, 2-Phosphabicyclo[2.2.2]octene derivative, 1,2,3,6-Tetrahydrophosphinine oxide,... 

Tetrahydrophosphinine-and 1,2,3,4,5,6-Hexahydrophosphinine Oxides with an Exocyclic P-Moiety... 

An overview is given on the synthesis, reactivity, and properties of six-membered P-heterocycles, such as 1,2-dihydro-, 1,2,3,6-tetrahydro- and 1,2,3,4,5,6-hexahydrophosphinine oxides, as well as bridged P-heterocycles, such as phosphabicyclo[2.2.2]octene derivatives and finally heterocyclic P -oxophosphoranes. 

Catalytic hydrogenation of dimethyl-dihydrophosphinine oxide 29 gave dimethyl-hexahydrophosphinine oxide 30 as a mixture of three isomers (30p 302 and 303) (Scheme 14) [28],... 

It is recalled that the dihydrophosphinine oxides (e.g. 10) are obtained by the thermolysis of phosphabicyclohexane oxides (e.g. 2). It was also possible to obtain hexahydrophosphinine oxides (31) directly from the phosphabicyclohexane oxides (2), but somewhat more forcing conditions had to be applied during the hydrogenation (Scheme 15) [29],... 

Catalytic hydrogenation of 2,4,6-trialkylphenyl- and 4-alkylphenyl-l,2-dihy-drophosphinine oxides (34) afforded, in most cases, the expected hexahydrophosphinine oxides (35). However, hydrogenation of the triisopropylphenyl starting... 

The preparation of the triisopropylphenyl-hexahydrophosphinine oxide (40) required alternative synthetic methods. In the first approach, introduction of the aryl group was attempted by substitution at the phosphorus atom. The 6-ring phosphinate (37) was converted to the corresponding phosphinous chloride (38) in two steps, whose reaction with the Grignard reagent followed by oxidation led, surprisingly, to a 9 1 mixture of an O-inserted species (39) and the desired product (40) (Scheme 18) [30],... 

According to another protocol, the double-bonds of the aryl-dihydrophosphinine oxide (5t) were subjected to a stepwise saturation. In the first step, the electron-poor a,P-double-bond of the starting material (5X) was reduced via hydroboration. The remaining unsaturation and the chlorine atom in 41 were removed by catalytic hydrogenation. This method was found to be more suitable for the preparation of the triisopropylphenyl-hexahydrophosphinine oxide (40) (Scheme 19) [30],... 

Selective reduction of electron-poor double-bonds was also extended to a 4-substituted-l,4-dihydrophosphinine oxide (43). Its a, 3-double-bonds could be reduced step by step to give eventually the 4-substituted hexahydrophosphinine oxide (45) that, on catalytic hydrogenation, afforded the corresponding trimethyl-hexahydrophosphinine oxide (46). The latter could also be obtained directly from 43 by catalytic hydrogenation (Scheme 21) [32],... 

The 3-diphenylphosphonoxido-l-phenyl-hexahydrophosphinine oxide (55, Z = Ph) was subjected to a similar sequences of reaction. The cis chelate complex (67) was obtained in a better yield as the consequence of the more flexible hexahydro-phosphinine ring (Scheme 30) [40], Stereostucture of the diphosphines and the possible complexes was evaluated by calculations. 

The recent developments in phosphinine chemistry including dihydro-, tetrahydro- and hexahydrophosphinine oxides were reviewed by Keglevich." ... 

The esterification of cyclic phosphinic acids such as l-hydroxy-3-phospholene oxides (7 and 8), 1-hydroxy-phospholane oxides (11 and 13), and l-hydroxy-l,2,3,4,5,6-hexahydrophosphinine oxide (15) was carried out in the presence of c. 15-fold excess of the alcohols in a closed vessel to afford the phosphinates (9,10,12,14, and 16) in acceptable to excellent (44-95%) yields [33-37]. The method elaborated seems to be of general value. It was foxmd that the esterification of phosphinic acids is thermoneutral and kinetically controlled, and also represented as an irreversible process [35]. 

The S3mthesis of another kind of bidentate P-ligand was based on the addition of >P(0)H species at the end of the a,p-double bond of 1,2-dihydrophosphinine oxides (42). As the double bond was not too reactive, the activation of the >P(0)H reagent by MesAl was necessary prior to the addition to obtain the 3-phosphono- ((R0)2P(0)-), 3-phosphinoyl- (Ph2P(0)-), and other related ((EtO)PhP(0)-)l,2,3,6-tetrahydrophosphinine oxides (43) (Scheme 15) [61,62]. Under MW irradiation, there was no reaction. The 3-substituted-l,2,3,6-tetrahydrophosphinine oxides (43) were converted to the fully saturated 1,2,3,4,5,6-hexahydrophosphinine oxides (44) by catalytic hydrogenation (Scheme 15) [63,64]. 

The 3-phosphinoyl-l-phenyl-l,2,3,6-tetrahydrophosphinine oxide (45) and the 3-phosphinoyl-l-phenyl-1,2,3,4,5,6-hexahydrophosphinine oxide (48) were converted to the corresponding c/s-chelate Pt complexes 47 and 50, respectively, after double deoxygenation followed by complexation by dichlorodibenzonitrile platinum (Scheme 16) [65,66]. 

G. Keglevich, M. Sipos, V. Ujj, T. Kortvelyesi, Synthesis of 3-phosphinoxido- and 3-phosphono-l,2,3,4,5,6-hexahydrophosphinine oxides as potential precursors of bidentate P-Ugands, Lett. Org. Chem. 2 (2005) 608-612. 

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