Heterocyclic phosphino

Synthesis and application of heterocyclic phosphino oxazoline (hetphox)... 

SYNTHESIS AND APPLICATION OF HETEROCYCLIC PHOSPHINO OXAZOLINE(HetPHOX) IRIDIUM COMPLEXES FOR THE ASYMMETRIC HYDROGENATION OF ALKENES... 

Benzannulated NHPs are straightforwardly accessible from AUV-disubsti luted o-phenylenediamines either via base-induced condensation with substituted dichlorophosphines [25] or PC13 [26], or via transamination with tris(dialkylamino) phosphines [13, 14, 27], respectively. An analogous NH-substituted derivative was obtained in low yield via transamination of o-phcnylcncdiaminc with ethoxy-bis(diethylamino)phosphine [28], and condensation of o-phenylenediamine with excess tris(diethylamino)phosphine furnished a l,3-bis(phosphino)-substituted heterocycle [29], Intermediates with one or two NH functions were detectable by spectroscopy but could not be isolated in pure form under these conditions. However, 2-chloro-benzo-l,3,2-diazaphospholene and the corresponding 1-phenyl derivative were prepared in acceptable yield via condensation of PC13 with o-phenylenediamine under microwave irradiation [30], or with A-phenyl-o-phenylenediamine under reflux [27], respectively, in the absence of additional base. The formation of tetrameric benzo-NHPs during transamination of A-alkyl-o-phenylenediamines with P(NMe2)3 has already been mentioned (cf. the section entitled 1,3,2-Diazaphospholes and 1,3,2-Diazaphospholides ). 

Figure 44 Structures of heterocyclic amino-, phosphino- and arsinogallanes 622, 626, and 627.

Similarly, the (phosphino)(silyl)carbene 2a reacts at -30°C with a slight excess of the tert-butylphosphaalkyne cleanly affording the 2-phosphino-2//-phosphirene 34.53 The reaction leading to 34 is strictly analogous to that observed on reacting the transient dichlorocarbene with the tert-butyl-phosphaalkyne, in which the 2//-phosphirene 36 was obtained.54 The three-membered heterocycle 34 appeared to be rather unstable and rearranged, quantitatively, to afford the lA5,2A3-diphosphete 35 after 3 h at room temperature.55 Once again, these results as a whole indicate that a concerted [1 + 2]-cycloaddition process is involved in the formation of the 2//-phosph-irene 34. 

The (phosphino)(silyl)carbene 2a has been shown to exhibit this diagnostic reactivity. Under rather drastic conditions (300°C, 10 2 mm Hg), 2a has been converted into the azaphospholidine 37, in high yield, as a mixture of four diastereomers, which result from the presence of three asymmetric centers.4 The high regioselectivity of the carbene insertion (no formation of a four-membered ring was detected) is intriguing, especially since the same regioselectivity is observed upon thermolysis of bis(diisopropyl-amino)phosphinodiazomethane li.4 Yet, in contrast, four-membered heterocycles were obtained with other phosphinocarbenes (Sections V,C,1 and 3). 

Vacuum thermolysis (160°C) of the hemiaminal 11 generates the azaphos-phetane 65 in 85% yield.32 This product clearly results from the intramolecular insertion of the transient (amino) (phosphino)carbene 2h into the C-H bond of a diisopropylamino group bonded to phosphorus. Note that the four-membered heterocycle 65 is formed exclusively in spite of the ratio of six methyl-CH bonds to one methine-CH bond, and that only one of the two possible diastereomers is detected. The same regio- and diastereo-selectivity have already been observed with the di(phosphino)carbene 2g,74 but is in marked contrast to the exclusive formation of five-membered rings... 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

Carbenes [74-76], and in particular W-heterocyclic carbenes (NHCs), are today the topics of very intense research [43 8]. Carbenes were originally considered as chemical curiosities before being introduced by Doering in organic chemistry in the 1950s [77], and by Fischer in organometallic chemistry in 1964 [5]. Eater, it was shown that the stability of carbenes could be dramatically enhanced by the presence of heteroatom substituents. After the discovery of the first stable carbene, a (phos-phino)(silyl)carbene, by Bertrand et al. in 1988 [78], a variety of stable acyclic and cyclic carbenes have been prepared. With the exception of bis(amino)cycloprope-nylidenes [79], all these carbenes feature at least one amino or phosphino group directly bonded to the electron-deficient carbenic center. 

Reactions related to cyclopropanation can also be carried out with (phosphino) (silyl)carbenes (I). For example, benzaldehyde reacts with la at 0 °C leading to the corresponding epoxide, again as only one diastereomer. Even more striking are the reactions with benzonitrile and tert-butylphosphaalkyne that lead initially to azirine and phosphirene. Both three-membered heterocycles subsequently undergo ring expansion reactions affording azaphosphete and diphosphete, respectively (Scheme 8.18). This reaction is a new route for the synthesis of heterocyclobutadienes, and this demontrates the usefulness of (phosphino)(silyl)carbenes (I) for the synthesis of novel species. 

In the last IS years, considerable progress has been made in the understanding of carbene chemistry by the direct observation of short-lived species or through the synthesis of stable versions. Our group published the synthesis of a phosphino silyl carbene, the first stable singlet carbene, in 1988 [1]. Three years later, Arduengo et al. reported the preparation and X-ray crystal structure of the first stable N-heterocyclic carbene [2]. 

Summary Trimethyl- and triisopropyl-silyl diazomethane derivatives have been used for the synthesis of new types of diazo derivatives including those featuring a heavier main-group element or a transition metal directly bound to the diazo-carbon. They are also precursors to a variety of stable nitrilimines and carbodiimides, and stable pseudo-diazoalkenes and carbenes. (Phosphino)(silyl)carbenes have been used in the synthesis of new types of heterocycle including some stable four-7c-electron four-membered derivatives. 

Starting from (silyl)(phosphino)diazomethane derivatives, stable pseudo-diazoalkenes and carbenes have been obtained. The diazomethylenephosphoranes are very reactive dipolarophiles but are also synthetic equivalents of naked carbon C . The stable carbenes react in a similar manner to their transient analogues, but also exhibit new reactions the synthesis of unsaturated three-membered heterocycles is particularly noteworthy. Ring expansion reactions involving the latter are of special interest since they afford novel non-antiaromatic four-7t-electron four-membered heterocycles. 

Many new tertiary phosphines have been prepared by synthetic elaboration of simpler organophosphines which does not involve the phosphorus atom. Chiral phosphines bearing heterocyclic substituents have been obtained by elaboration of arylphosphines bearing amino, carboxaldehyde or nitrile groups, respectively, giving, e.g. the pyrrolidinyl system (147), phosphino-oxazolidines, e.g. (148), phosphino-oxathianes, e.g. (149), phos-phino-oxazines (150), and the phosphino-oxazolines (151). Wittig reac-... 

Phosphacycles and phosphino-substituted heterocycles as chiral ligands in asymmetric catalysis 03MI107. 

Krug, H.G., Neidlein, R., Krieger, C., and Kramer, W., Synthesis of phosphono- and phosphino-substituted six-membered heterocycles. Heterocycles, 38, 2695, 1994. 

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