Phosphane Imine

Azide konnen uber die Phosphan-iminc zu Nitro-Verbindungen umgcsetzt werden. Hierzu werden die Azide mit Triphenylphosphan (Staudinger-Reaktion) umgesetzt und die Phosphan-imine mit Ozon in Dichlormethan bei — 78n behandelt4 ... 

Allenic esters such as 185 can act not only as dipolarophiles but also, at least formally, as 1,3-dipoles, which was shown by Xu and Lu during the phosphane-cata-lyzed reaction with N-tosylimines 387 (Scheme 7.52) [358, 359]. The heterocycles 388 are formed at least in moderate and mostly in excellent yields, if R1 is an aryl or a vinyl group. The formation of the products can be explained by reversible nucleophilic addition of the phosphane to 185 (cf. Section 7.3.1) followed by nucleophilic addition of the resulting intermediate to the imine 387. 

Alkylidene-phosphapyrazolines 98-101 are much more thermally stable than their relatives 88, which do not possess the exo-methylene substitution. Dediazo-niation of 98 required heating in toluene at 110°C and gave one or more of the following products, probably via intermediate diphenylmethylene(vinylidene)phos-phoranes methylenephosphiranes, (2-siloxyvinyl)phosphanes, 2//-l,3-oxaphos-pholes, and l-alkylidene-2,3-dihydro-l//-benzo[c]phospholes (169). Thermolysis of 100 ( R = t-Bu, 1-adamantyl) afforded isolable 2-phosphabutadienes (169). The photochemical elimination of N2 from 98 generated cyclic azomethine imine dipoles 104 (Scheme 8.24), which rearrange to compounds 105 and 106 that could be further trapped with DMAD to form 107 (170). 

Attempts to prepare the A -benzylimine of hexafluoroacelone by treatment of the latter with (benzylimino)triphenyl-/. ,-phosphane give. /V-benzylidene-1,1,1,3,3,3-hexafluoropropan-2-amine [(CF,)2CHN = CHPh] in 56% yield, which results from complete isomerization of /V-benzyl-2,2,2-trifluoro-l-(trifluoromethyl)ethanimine [(CF3)2C = NCH,Ph] under the reaction conditions.12 Taking this into account, the reactivity of substituents R at the imine carbon of compounds 14 follows the order perfluoroalkyl > > aryl > > hydrogen > alkyl benzyl.14 11 as described below, alkoxycarbonyl as the R group in structure 14 (x-oxo ester derivatives) activates as effectively as perfluoroalkyl. 

Patel and Jamison [40] reported a catalytic three-component coupling of alkynes, imines, and triethylborane using a Ni complex and (S)-(+)-(neomenthyl)diphenyl-phosphane [(S)-NMDPP] 159 forming the alkylative coupling product (Scheme 9.28). No yields were reported. 

Lewis acid and the oxygen atom of the phosphane oxide, respectively. With this catalyst system, N-allyl- and N-benzhydrylimines generally gave lower enantioselectivities. The addition of phenol was found to have a beneficial effect on the reaction rates. The JandaJEL -supported bifunctional catalyst of 14 has also been shown by Shibasaki and co-workers to promote the Strecker-type reaction of aromatic and a,/ -unsaturated imines in excellent yields with 83-87% ee in the presence of tert-butanol (110%) [11]. The reactivity of the Janda/EL catalyst was comparable to the homogeneous analogue 14, and the catalyst could be recycled at least four times. 

Acyl- -imine E19b, 1258 (Wolff-Umlagerung/ + Phosphan-tmid)... 

When the W-trimethylsilyltris(2-pyridyl)phosphinimine (22) was treated with one equivalent of methyllithium at - 78°C, a lithium complex (23) binding a dipyridyl moiety with a trivalent amino-methyl (2-pyridyl)phosphane was isolated. This compound results from a ligand coupling process taking place on the pentacoordinate phosphorus intermediate formed by addition of methyllithium on the imine bond. 

Apart from phosphanes, typical systems used as chiral ligands in catalysis are alcohols, amines, amino alcohols and other N-functionalities including imines, amides and N-modificd carbonyl groups. Dicarbonyl compounds and their chirally modified equivalents such as dioximes or crown ethers, as well as sulfoxides, arsines, and cyclopentadienyl ligands with chiral side chains have been used. 

Scheme 3.78 Phosphane catalyzed [3 + 2] cycloaddition of 6-oxodienoates and imine...

Ir(I)-oxazolinyl-phosphane complexes are also effective catalysts for hydrosilylation of imines (246). Chiral poisoning of iridium complexes containing racemic DIOP with PRONOP provides an enantioselective catalyst (247). Iridium complexes containing phosphinooxazoline or dithioether ligands (like DIOSPr or DIOSPh) catalyze the enantioselective hydrogenation of functionalized olefins (248). 

Since simple ketones typically coordinate more weakly to metals than olefins, many Rh-phosphane complexes may show poor activity for the hydrogenation of simple ketones. However, the catalytic properties of cyclometalated half-sandwich Rh(lII) complexes 99-101, isolated or prepared in situ firom metal precursors and optically pure secondary amines, were evaluated, among which the complex 100 showed the highest productivity in the reduction of acetophenone with a i-PrOH/t-BuOK reductant system (Fig. 26) [93]. The complex 99 afforded good yield of alcohol products from acetophenone, but the enantioselectivity was low, while the cyclometalated imine 101 was almost inactive. The rhodacycle 100, which was formed in situ, efficientiy catalysed the reduction of substrates 102 (92 % ee), 103 (93 % ee) and 104 (91 % ee), with substrate 103 showing total chemoselectivity. For substrates 105,106 and 107, however, lower ee values were observed (<85 %). 

The method was quite efficient when several imine substrates with different protective groups were screened, with the nosyl derivatives (p-nitrophenylsulfonyl groups) being the best substrates. In the case of chelating bi-phosphane ligands (such as 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (BINAP)), the arylation was very slow, showing remarkable preference for mono-phosphane... 

As far as we are aware, there have been no other reports on the arylation of imine substrates with ruthenium catalysts, besides our own work. In 2012, we published our efforts at developing a Ru-catalyzed asymmetric catalytic imine arylation with organoboron reagents and with chiral phosphane and new NHC-type ligands (Scheme 6.33) [44]. 

In the same area, these authors have also investigated the efficiency of various chiral sterically congested phosphane-amide bifunctional organocatalysts with a binaphthyl scaffold in asymmetric aza-Morita-Baylis-Hillman reactions of A -sulfonated imines with activated olefins such as methyl and ethyl vinyl ketones." The corresponding aza-Morita-Baylis-Hillman adducts could be obtained in moderate to excellent yields (37-98%) and moderate to good... 

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