Phosphino alkenes

Marks and Douglass recently reported organolanthanide-catalyzed hydrophosphina-tion/cyclization of phosphino-alkenes and -alkynes (Scheme 5-15). 

Unlike the late metal chemistry reviewed above, these reactions did not require Michael acceptor substrates, but the reactions were rather slow (turnover frequencies range from 2 to 13 h at 22°C). For phosphino-alkenes (Scheme 5-15, Eqs. 1-3), a competing uncatalyzed reaction gave six-membered phosphorinane rings (Scheme 5-15, Eq. 6) this could be minimized by avoiding light and increased temperature. For phosphino-alkynes (Scheme 5-15, Eqs. 4 and 5), the products were unstable and could not be isolated [14]. 

The amide [Sm(45a) N(SiMe3)2 ] was a catalyst for an aUene-based hydroamination/ cyclisation. As an illustration, one such product upon hydrogenation yielded a naturally occurring alkaloid. Scheme 4.8. " " The same samarium(lll) amide was also active for the intramolecular hydrophosphination/cyclisation of phosphino-alkenes or -alkynes e.g., H2P(CH2)3C=CPh was transformed into 76. " ... 

The (phosphino)(silyl)carbene 2a readily and cleanly adds to benzalde-hyde and cinnamaldehyde, affording the oxiranes 27 and 28, as single diaste-reomers.40 These results strongly suggest a concerted mechanism, since the formation of a zwitterionic intermediate, such as 29, would result in the formation of a phosphoryl alkene via oxygen atom attack at the phosphorus center. Note that 2a does not react with ketones, which is in line with its nucleophilic character. 

Thus examples such as 16 that have a phosphino substituent on the N atom are more nucleophilic in character and react readily with electron-poor alkenes and alkynes (see above) but fail to react with those that are electron rich. In contrast, the ones with a phosphonio substituent (e.g., 24) were found to react readily with... 

In marked contrast, we used the cyclopropanation reaction of (phosphino)(silyl)-carbene (la) with methyl acrylate to demonstrate the carbene nature of our compound. More recently, we studied in detail the stereochemistry of this type of reaction.The (phosphino)(silyl)carbene (la) reacted efficiently with 3,3,4,4,5, 5,6,6,6-nonafluorohex-l-ene and (Z)- and ( )-2-deuteriostyrene giving the corresponding cyclopropanes in good yields. The stereochemical outcome was such that all monosubstituted alkenes gave exclusively the syn isomer (with respect to the phosphino group), and the addition of disubstituted alkenes was totally stereospecific (Scheme 8.16). 

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

It should be mentioned that alkenes 236, which are often found as (formal) carbene dimers in reactions involving electrophilic carbenes, have never been observed in the context of phosphino(silyl)carbenes. UV-irradiation of a [bis(dialkylamino)phosphino] (trimethylsilyl)diazomethane leads to a l(A5),3(k5)-diphosphete 237 (equation 80) which can be regarded as the head-to-tail cyclodimer of a phosphavinyl ylide (cf 232B), whereas irradiation of diphenylphosphino- or dunethoxyphosphino-(trimethylsilyl)diazomethane produces a l,2(k5),4(k5),6(X5)-azatriphosphorin 238 in a sequence which may also include the corresponding diphosphete 237138. 

It was shown earlier that palladium-catalyzed hydrovinylation of styrene using phosphino ester-type ligands leads to isomerization of the external al-kene (kinetic product) to the internal alkene (thermodynamic product) at higher substrate conversion. In this regard, the idea was to suppress this isomerization by running the reaction at lower conversion in a CFMR system in order to minimize the catalyst-substrate contact time. 

Ruthenium complexes of chiral phosphines notably BINAP, 2,2 -bis(diphenyl-phosphino)-l,l -binaphthyl are very useful for industrial hydrogenations and H-transfer hydrogenation of alkenes and ketones. This is due to high turnover numbers and enantiomeric excesses (ee) of the products. A specific example41 of an... 

Zhong et al. used their phosphino functionalised carbene ligands successfully in the palladium catalysed hydroarylation of bicyclic alkenes. 

The reaction of cyanomethyllithium with 2,4,6-tri-t-butylphenyl-dichlorophosphine enables a one-step preparation of the functionalised phospha-alkene (144). A new route to phospha-alkenes is provided by nucleophilic attack at the vinylic CH2 of the halogenophosphine (145), with displacement of halogen from phosphorus. Thus, with DABCO as nucleophile, the novel system (146) is formed.Treatment of the phosphino-substituted ylides (147) with Lewis acids results in the 2-phosphonio-l-phospha-alkenes (148), reported to be sufficiently stable for X-ray analysis, but also undergoing various addition reactions. 

Chelation-assisted additions of formyl C-H bonds to olefins and dienes have been reported by Jun et al. [120]. In the case of the reaction of 8-quinolinecar-boxaldehyde, they proposed that the formation of the stable 5-membered met-allacyclic complex [121] suppressed the undesired decarbonylation reaction (Eq. 53) [120]. The intermolecular hydro acylation of 1-alkene with 2-(diphenyl-phosphino)benzaldehyde by rhodium(I) catalyst has been conducted on the basis of this working hypothesis [122]. 

Palladium catalysts with chiral monodentate phosphine ligands, (5)-2-diphenyl-phosphino)-2 -alkoxy-1,1 -binaphthyl (MOPs), are extremely efficient for the asymmetric hydrosilylation of 1-alkenes with HSiCls, Reaction is carried out at 40°C for... 

---