Dihydrophosphinine oxides

The reaction of 1,2-dihydrophosphinine oxides 150A and 150B with tetra-cyanoethylene (TCNE) does not follow the Diels-Alder reaction, but rather follows the reaction of two moles of dihydrophosphinine (both of the two double bond isomers) with one mole TCNE to give a 2 1 cyclic adduct, via the 1 1 adduct, due to the ionic or radical nature of TCNE. The... 

Scheme 49 Reaction of 1,2-dihydrophosphinine oxides with tetracyanoethylene to form 151...

Diels-Alder reactions form a well-studied group of MW-assisted reactions (Keglevich et al., 2007). The cycloaddition of 1,2-dihydrophosphinine oxides and dimethyl acetylenedicarboxylate (DMAD) or A-phenylmaleimide (NPMI) results in the formation of 2-phosphabicyclo octadiene and bicyclooctene, respectively. Under traditional heating in boiling toluene, the reaction was rather slow. On MW irradiation at 110°C in the absence of any solvent, the cycloaddition became 30 times faster... 

Diels-Alder dimerisation of 1,2-dihydrophosphinine oxides has also been reported, giving new 2-phosphabicyclo[2,2,2]oct-5-ene-2-oxides, e.g.,... 

The Diels-Alder reaction of 1,2-dihydrophosphinine oxides with dienophiles, such as acetylenic derivatives and maleic acid derivatives affords 2-phosphabicyclo [2.2.2]octadiene and 2-phosphabicyclo[2.2.2]octene 2-oxides that may be regarded as the precursors of low-coordinate, methylenephosphine oxides that are useful in the phosphorylation of 0- and N-nucleophiles. It was observed that the photo-chemically induced fragmentation-related phosphorylation may follow a novel addition-elimination mechanism instead of the classical elimination-addition protocol. 

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,... 

It was quite interesting that in the case of 3 having a 2,4,6-triisopropylphenyl substituent on the phosphorus atom, partial opening of the cyclopropane ring of the initially formed phosphabicyclohexanes (4t and 42) resulted in the corresponding 1,2-dihydrophosphinine oxide (52) (Scheme 2) [18],... 

Dihydrophosphinine oxides served as excellent starting materials to more saturated derivatives. First of all, the dihydrophosphinine oxides (27) were subjected to catalytic hydrogenation to furnish diastereomeric mixtures of 1,2,3,4,5,6-hexahy-drophosphinine oxides (28). The reaction involves reduction of the double-bond and hydrogenolysis of the C-Cl bond (Scheme 13) [28],... 

The 1,2-dihydrophosphinine oxide (5,) —> 1,2,3,6-tetrahydrophosphinine oxide (41) transformation shown in Scheme 19 was found to be of general applicability. A variety of P-substituted dihydrophosphinine oxides (14) were converted to tet-rahydrophosphinine oxides (42) by the addition of borane to the reactive a,P-double-bond followed by hydrolysis of the boryl intermediate so obtained (Scheme 20) [31]. 

The 1,2-dihydrophosphinine oxides are versatile intermediates [4,5] and are suitable to take part in Diels-Alder reaction with different dienophiles, like N-phenyl maleimide and dimethyl acetylenedicarboxylate (DMAD) [47]. These cycloadditions were also performed on MW irradiation in the absence of any solvent. Starting from the 1-phenyl-dihydrophosphinine oxide (23), the reactions were 25 times faster as compared to the thermal variations, and the valuable cycloadducts 2-phosphabicyclo[2.2.2]octene 24 and 2-phosphabicyclo[2.2.2]octadiene 25 were obtained in excellent yields with high purity (Scheme 8) [48]. 

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]. 

G. Keglevich, R. Kovacs, L. Drahos, Diels-Alder cycloadditions of 1,2-dihydrophosphinine oxides and fi agmentation-related phosphorylations with 2-phosphabicyclo[2.2.2]octadiene oxides under green chemical conditions - the role of microwave and ionic liquids. Phosphorus Sulfur Sfflcon 186 (2011) 2172-2179. 

The Keglevich group has continued to deal with environmentally friendly and P-heterocyclic chemistry. The solid liquid phase alkylation of P=0-functionalised CH acidic compounds was accomplished under phase transfer catalytic and microwave (MW) conditions." a-Hydroxy-benzylphosphine oxides were synthesized by the addition of diphenylphosphine oxide to the carbonyl group of substituted benzaldehydes under MW conditions." The double Kabachnik-Fields (phospha-Mannich) reaction was utilized in the preparation of bis(phosphinoxidomethyl)amines. The Diels Alder cycloadditions of 1,2-dihydrophosphinine oxides and subsequent... 

The unexpected observation that the interaction of l-(2,4,6-triisopropylphenyl-l, 2-dihydrophosphinine oxide and dimethyl acetylenedicarboxylate resulted in a... 

Thermolysis of the tri-te/t-butylphenyl phosphabicyclohexane (12) led to dihydrophosphinine oxides 13t and 132. As can be seen, the opening of the cyclopropane ring was accompanied by the loss of the te/t-butyl group in position 4 (Scheme 7) [16],... 

Changes in the P-functionality of the dihydrophosphinine oxides (14) made available phosphine sulfides and phosphine boranes (15 and 16, respectively) (Scheme 8)[19, 20],... 

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],... 

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],... 

Dichloromethylene-l,4-dihydrophosphinine oxide (43) was subjected to a similar sequence of reactions to afford the analogous Rh(III) complex (62). In this particular case, the phosphine (61) was also utilized in the preparation of a palladium(II) complex (63) (Scheme 28. The complexes were tested in the hydro-formylation of styrene [38],... 

The dihydrophosphinine oxides (14) could easily be involved in Diels-Alder reactions with different dienophiles, such as dimethyl acetylenedicarboxylate (DMAD) and maleic derivatives, like A-phenylmaleimide to give the corresponding... 

Another unit of the dihydrophosphinine oxide (14) was applied as the dienophile in the [4 + 2] cycloaddition yielding dimer 71[46, 47] (Scheme 31). Reaction of the dihydrophosphinine oxides with 4-phenyl-1,2,4-triazoline-3,5-dione gave 7,8-diazaphosphabicyclo[2.2.2]octenes (72) as the first examples of this family of compound (Scheme 31)[45, 48],... 

Scheme 29 Preparation of 1,2- and 1,4-dihydrophosphinine oxides 142 and 143, and 1,2,3,6-tetrahydro analogues 144 and 145...

E. Hohmann, G. Keglevich, 1. Greiner, The effect of onium salt additives on the Diels Alder reactions of a l-phenyl-l,2-dihydrophosphinine oxide under microwave conditions, Phosphorus Sulfur Silicon 182 (2007) 2351-2357. 

The Pd-catalyzed intramolecular arylation of benzyl-diaiylphosphine oxides led to l-aryl-dibenzo-l,2-dihydrophosphinine oxides (Scheme 49). An interesting synthesis of 6/f-naphtho[2,3-c]chromenes was developed by the Pd-catalyzed reaction of 2-haloaryl-allenes with 2-alkynylphenols. The procedure is demonstrated by a simple example (Scheme 50). ... 

Regioisomeric 1,2-dihydrophosphinine 1-oxides 21A, 21B, and 24 undergo the Diels-Alder cyclization with dimethyl acetylenedicarboxylate (DMAD) to give 2-phosphabicyclo [2.2.2] octane derivatives 22A, 22B, and 25 (Schemes 7 and 8). The 1,2-dihydrophosphinine 1-oxides 26 react with phenylmaleimide to give the corresponding tricyclic heterocycles 27 (four isomers) (Scheme 9). 

Scheme 7 Regioisomeric 1,2-dihydrophosphinine 1-oxides 21A and 21B undergo the Diels-Alder cyclization with DMAD to give 22A and 22B...

Scheme9 1,2-Dihydrophosphinine 1-oxides 26 react with phenylmaleimide to give the corresponding tricyclic heterocycles 27...

Phosphabicyclo[3.1.0]hexane 3-oxides 40A and 40B and dihydrophos-phinine 1-oxide derivatives, 1,6-dihydro- and 1,2-dihydrophosphinine deriva-... 

A series of 3-phosphinoxido- and 3-phosphono-l,2,3,6-tetrahydrophosphinine oxides (47) was synthesized by the addition of diphenylphosphine oxide and dialkyl phosphites on the electron-poor a,p-double-bond of 1,2-dihydrophosphinine... 

The addition of dichlorocarbene to the 1,2-dihydrophosphinine-l-oxides (5 Y = MeO, Ph) under phase transfer conditions, followed by alkaline dehydrochlorination of the intermediate (6 Y = MeO, Ph), afforded the phosphepin-1-oxides (7 Y = MeO, Ph) in 3-5% yields <87JOC3983>. A number of related compounds have been prepared similarly <93S93l>. 

Bicyclo[3.1.0]phosphine oxide 7 also gave a diastereomeric mixture of the six-membered phosphine oxide 11 in 70% yield and not the five-membered ring product (Scheme The hydrogenolysis proceeded through the mixture of dihydrophosphinines. 

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