Stereogenic phosphorus

Hindered rotation around the P-N bond has been observed at low temperature in tetrasubstituted phosphorus amides [28]. For PhjPNJSiMCjJj, two different Me3Si groups are observed below -65 °C, the calculated activation energy for P-N rotation being 10.2 Real moT [29]. Chiral phosphinous amides with stereogenic phosphorus atoms have been prepared [30,31 ]. 

The fourth chapter Selected Five-Membered Phosphorus Heterocycles Containing a Stereogenic Phosphorus presents the description of the synthesis and use of these compounds in a few asymmetric syntheses. 

Selected Five-Membered Phosphorus Heterocycles Containing a Stereogenic Phosphorus... 

Abstract This review presents the synthesis of selected five-membered phosphorus heterocycles containing a stereogenic phosphorus in an optically active form. Their utility in a few asymmetric reactions is also briefly mentioned. 

A-trityl-(l/ ,2S)-norephedrine (58), the corresponding allyl phosphonates 62a,b were obtained via the Arbusov rearrangement of 2-ethoxy-1,3,2-oxazaphospholidine 60. The absolute configuration of the major diastereomer, 62a was determined by X-ray as (2S1,45,51 ).The reaction of the major diastereomer of allyl phosphonates 61a and 62a with DBU afforded the corresponding vinylphosphonates 63a,b (Scheme 21) [48], Nucleophilic addition to these resulted in induction of chirality at the [1-position of the stereogenic phosphorus atom in the initially produced diastereomeric phosphonates 64 or 65 (Scheme 21) [48],... 

Advances in the use of anionic stereogenic phosphorus have been interesting. Acylation of lithium o-anisylphenylphosphide with chloro-formates bearing chiral alkyl groups provided a diastereomeric mixture that could be induced to undergo an inversion at phosphorus (at relatively low temperature) to form the more favorable diastereoisomer in a crystalline lattice.186 Subsequent conversion to the quaternary phos-phonium species was followed by removal of the acyl group and isolation of the chiral tertiary phosphine as the borane derivative (Equation 3.10). 

The first example for the use of a diphosphine bearing stereogenic phosphorus atoms as a ligand in copper-catalyzed Michael additions has been reported by Inamoto and co-workers,265,265a who showed that the reaction of cyclohex-2-enone and the corresponding seven-membered enone with diethylzinc in the presence of Cu(OTf)2 and 307 (abbreviated as MiniPHOS) gave rise to the formation of the addition products with 70% and 97% ee, respectively (Scheme 84). The corresponding transformation of chalcone proceeded with 71% ee. Other simple diphosphines, however, displayed only moderate enantioselectivities in copper-catalyzed Michael additions.226... 

In the meantime, Knowles and his colleagues had prepared and tested different chiral phosphines with stereogenic phosphorus atoms. It was thought that asymmetry needed to be as near as possible to the metal because the catalytic reaction takes place in the coordination sphere of the metal the substituents on the phosphorus were varied and the best results were obtained when phosphines such as the o-anisyl(methyl)phenylphosphine (PAMP) and o-anisyl(cyclohexyl)methylphosphine (CAMP) were used (Figure 12). 

It is interesting to note that benzeneseleninic acid (92) was found [48] to behave as a very stereoselective oxidant of optically active methylphenyl-n-propylphosphine sulfide (97a) and methylphenyl-n-propylphosphine selenide (97b). The corresponding phosphine oxide 98 was formed with almost full inversion of configuration at the stereogenic phosphorus atom (Scheme 11). 

The catalyst is a cationic complex of rhodium with another diphosphine, DIP AMP. DIP AMP s chirality resides in the two stereogenic phosphorus atoms unlike amines, phosphines are conhgura-tionally stable, rather like sulfoxides (which we will discuss in the next chapter). The catalyst imposes chirality on the hydrogenation by coordinating to both the amide group and the double bond of the substrate. Two diastereoisomeric complexes result, since the chiral catalyst can coordinate to either of the enantiotopic faces of the double bond. 

Asymmetric syntheses of compounds containing stereogenic phosphorus centers (reactions with participation of phospholes) 04ACR169. 

Selected phosphorous heterocycles containing a stereogenic phosphorus... 

Compund 78 is among the new transition metal catalysts that have found good use in the decomposition of diazo compounds and delivery of the metal carbenoids to alkenes." Iminodiazaphospholidine (79) possesses a stereogenic phosphorus center and its applicability to effect asymmetric cyclopropanation" is now known. The Zn chelate of 80 is effective for the Simmons-Smith reaction of allylic alcohols. ... 

Brunei, J.M., Legrand, O., Reymond, S. and Buono, G. (1999) First iminodiazaphospholidines with a stereogenic phosphorus center. Application to asymmetric copper-catalysed cyclopro-panation. Journal of the American Chemical Society, 121, 5807-5808. 

Recent Advances in Asymmetric Synthesis of P-Stereogenic Phosphorus Compounds... 

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