Cyclic phosphonamidates

The structures of the salts (131)168 and (132),159 a chelated ylide,160 and the insecticide coroxon161 have been determined. The structures of the cis- and trans-isomers of the cyclic phosphonamide (133) differed in that the cw-isomer has a half-chair conformation whereas the trans-isomer has an envelope conformation. Both compounds had hydrogen bonds of approximately 269 pm.162 The phosphadiazane (134)... 

Cyclic phosphonamides (tetrahydro-2//-l, 3,2-oxazaphosphorine 2-oxides) were obtained by reaction of / -amino alcohols with benzylphosphonic dichloride in moderate yield. In the case of the 6-monomethyl derivative the diastereomers were separated by chromatography. Deprotonation with /erz-butyllithium followed by alkylation occurred in a highly stereoselective manner (d.r. 96 4-99 1), independent of the nature of the alkylating reagent, counterion and solvent, as demonstrated for the 6,6-dimethyl derivative6. 

A comparison of the reactivity of C-N or C-P fission in P-lactams and four-membered cyclic phosphonamidates, respectively, shows the latter to be much more reactive (95PAC711). The absolute configuration of some 1,3,4-trisubstituted P-Iactams is determined by CD spectra (95TL4217). A ring expansion of 3-amido-l-hydroxy-p-lactams to 4-imidazolin-2-ones by the action of tosyl chloride and organic base is reported (95TL1617). 

Hence, equatorial attack seems the most reasonable and simplest way to describe approach of the nucleophile at 90° to the leaving group, leading to the most stable pentacoordinate intermediate. However, it is also possible to postulate a square pyramidal structure such as 104 as a transition state that would change into intermediate 101 (Scheme 27). Such a structure was previously proposed in phosphorus chemistry by Hudson et al. to explain the alkaline hydrolysis of cyclic phosphonamidates. 

Cyclic phosphonamide a-carbanions are excellent olefination reagents particularly useful for enolizable carbonyl compounds. P-stabilized allyl anions have found application as Michael donors. " ... 

Even a remote Boc-NH unit exerts a directing effect on the lithiation at a benzylic r< sition. Cyclic phosphonamidates form stabilized carbanions that react with elec-Tophiles stereoselectively. A bulky (e.g., f-Pr) group on the nitrogen atom impedes ne approach of the reagents from its side. ... 

This reaction has been modified to start with cyclic phosphonamides via the reaction between phosphonyl dichloride with diamines." ... 

Related catalysts for asymmetric borane reduction of ketones are open chain and cyclic phosphoric amides, in the oxidation state +3 or +5 (Scheme 11.3) [10, 11]. Early examples are the phosphonamides and phosphinamides 5a and 5b of Wills et al. [12] and the oxazaphospholidine-borane complex 6a of Buono et al. [13]. In the presence of 2-10 mol% catalysts 5a,b, co-chloroacetophenone was reduced by BH3 SMe2 with 35-46% ee [12]. For catalyst 6a a remarkable 92% ee was reported for the catalytic reduction of methyl iso-butyl ketone and 75% ee for acetophenone... 

Preliminary X-ray data on the carcinostat isophosphamide (56 R ClCHjCHj) show that the conformation about phosphorus is the same as in its better known isomer phosphamide (57).Important new mechanistic information has been obtained from kinetic measurements on the alkaline hydrolysis of cyclic phos-phoramidates (58) and phosphonamidates (59), in the latter the data are... 

Assorted anions. These are generated by deprotonation of allylic halides," chloromethylphosphonic esters, conjugated hydrazones, chiral carbamates,unsaturated a-aminonitriles, phosphonamides," and sulfonamides. The dianions derived from tu-haloalkanecarboxylic acids cyclize, and this reaction forms the basis of a synthesis of V-Boc cyclic imino acids. The conjugate bases of 2-(arylmethoxy)-methyl-2-oxazolines are unstable as [2,3]sigmatropic rearrangement takes place even at — 75°C. 

An early study on the hydrolysis of the cyclic phosphoramidate [65] in base demonstrated exclusive endocyclic P—O bond cleavage, in contrast with the P—N bond cleavage observed for the corresponding phosphonamidate [66] (Brown et al., 1976) (Scheme 24). This observation is consistent with the similar apical potentialities of oxy and azo ligands derived by Hall and Inch in their elegant stereochemical studies of similar cyclic compounds (p. 144). 

To a stirred solution of 0.628 g cyclic allyl phosphonamide (3.61 mmol) in 10 mL tetrahydrofuran was added 2.4 mL 1.6 M n-butyllithium (3.84 mmol) at -78°C under argon. After 0.5 h, 0.285 g methyl ethyl ketone (4.18 mmol) was added. Water (0.2 mL) was added after an additional 10 min, and the solution was allowed to warm to room temperature, whereupon the reaction mixture was diluted with 100 mL methylene chloride and filtered through a glass wool plug. The solution was dried over sodium sulfate and filtered, and the solvent was evaporated under vacuum at room temperature to yield 0.816 g of a sticky yellow syrup containing some residual methylene chloride. 

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