SEGPHOS-Pd

Scheme 20 Enantioselective ene-type spiro cyclization of 1,6-enyne catalyzed by cationic (P)-SEGPHOS-Pd(lI) complexes...

Scheme 39 Ene reaction catalyzed by cationic SEGPHOS-Pd(II) complex...

An asymmetric and catalytic Conia-type Alder-Ene reaction has been reported using a combination of asymmetric Pd ligand [(DTBM-SEGPHOS)Pd(OTf)2, 171] and Yb(OT 3 with AcOH. The reactions are quite dilute, yet both conversion and optical purity were good for the p-keto ester or differentiated p-diketone substrates 172. 

The axially chiral (allenylmethyl) silanes 110 were also prepared in optically active form using chiral Pd catalysts [98]. For the asymmetric synthesis of 110, a Pd/(R)-segphos system was much better in terms of enantioselectivity than the Pd/(R)-binap catalyst. Under the optimized conditions, 110m and llOt were obtained in 79% ee (57% yield) and 87% ee (63% yield), respectively (Scheme 3.56). The enantio-merically enriched (allenylmethyl) silanes 110 served for Lewis acid-promoted SE reaction with tBuCH(OMe)2 to give conjugated dienes 111 with a newly formed chiral carbon center (Scheme 3.56). During the SE reaction, the allenic axial chirality was transferred to the carbon central chirality with up to 88% transfer efficiency. 

The syntheses of chiral 3-substituted sultams 159 and 161 have been achieved through the asymmetric hydrogenation of their corresponding cyclic A -sulfonylimines 157 and 160 by making use of the Pd/bisphosphine complex (S)-SegPhos 158 <07JOC3729>. 

The carbonyl-ene reaction is a source of homoallylic alcohols, although the scope is somewhat limited. Synthesis of chiral tertiary a-hydroxycarboxylic esters from glyoxyUc esters has been studied, and many metal catalysts of varying degree of effectiveness have been identified. The Ag-catalyzed reaction between enol silyl ethers and a glyoxylic ester is stericaUy controlled by the Pd-SEGPHOS complex. ... 

The organopalladium species generated from coupling reaction of ArB(OH)2 with an allene is readily trapped by a properly distanced carbonyl group. Accordingly, 5,6-alkadi-enals are transformed into cw-2-(a-styryl)cyclopentanols. Adding (5)-SEGPHOS to complex the Pd salt has the desirable effect of asymmetric induction. ... 

Indenols. Coupling between o-formylarylboronic acids with alkynes leads to indenols. The catalyst system includes Pd(OTf)2 2H2O and Me4-SEGPHOS ligand. ... 

Currently, a significant body of work deals with the use of chiral cationic palladium complexes bearing ligands of the BINAP type or related bisphosphine ligands such as SEGPHOS (Fig. 3). These are based on the pioneering work from Sodeoka on the direct formation of chiral palladium enolate complexes from the palladium precursors and 1,3-dicarbonyl compounds [10, 23]. Within this context, the combination of cationic BINAP-Pd complexes and N-fluoro-bis(phenylsulfonyl)imine (NFSI) was introduced by Sodeoka for the realization of an extremely efficient a-fluorination of 3-keto esters (Scheme 5). 

The attention is now turned to the asymmetric synthesis of six-membered rings because substrates 1 led to achiral products via p H elimination although the intermediates could be enantiomerically enriched. Pd(ll)/(S)-BINAP systems were applied to the substrate 4 with trisubstituted olefin to give the cyclized product 5 with 26% ee in 25% yield (Scheme 10). (S)-SEGPHOS was more effective than BINAP to afford 5 with 56% ee. Moreover, the enantioselectivity dramatically increased up to 76% ee by using sterically demanding (S)-Xyl-SEGPHOS. 

The asymmetric Friedel-Crafts reaction of trifluoromethyl pyruvate 53 with aromatic compounds is catalyzed by cationic Pd(II) complexes with BINAP or SEGPHOS [184]. The reaction proceeded at -30 °C to afford the product 63 in 89% ee with (S)-BINAP and in 82% ee with (S)-SEGPHOS (Scheme 45). In sharp contrast to the situation of the carbonyl-ene reaction, the BINAP ligand provides higher enantioselectivity than the SEGPHOS ligand. 

Ene reaction of 26 with ethyl trifluoropyruvate (29) proceeded with high enan-tioselectivity using the dicationic Pd catalyst prepared by the reaction of SEGPHOS (XIV-3)-PdCl2 with AgSbFg to give 30 with 96% ee quantitatively [8]. 

The atropisomeric diphosphanes Binap, Hg-Binap, Segphos also led to very efficient and selective catalysts associated to Pd(02CCF3)2 [18] or [Pd(MeCN)4] [BF4]2/HC02H [19]. In the presence of rhodium catalysts, depending on the nature of the starting enyne, several diphosphanes such as Me-Duphos, Binap, Biphemp were efficiently used [20]. 

Fig. 10.12 Enantioselective formation of a tetrahydropyran ring from a 1,6-enyne, promoted by a Pd-Xylyl-SEGPHOS catalyst [24]...

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