PPFA-palladium

Cross-coupling of o-trimethylsilylbenzylmagnesium bromide with alkenyl bromides catalyzed by the PPFA-palladium complex gave optically active allylsilanes 11 (eq. 6). Allylsilane 11a reacted enantioselectively with the prochiral carbonyl compounds 12 in the presence of TiCl4 to produce alcohols 13 of over 90% enantiomeric purity (eq. 7). ... 

Linear 1,3-dienes have also been subjected to the palladium-catalyzed asymmetric hydrosilylation (Scheme 12, Table 5). Reaction of 1-phenyl-l,3-butadiene 46a with HSiClj catalyzed by palladium-(/ )-(A)-PPFA 5a gave a mixture of regioisomeric allysilanes 47, and 48 and 49, in a ratio of 94 to 6, the major isomer 47 and the minor isomer 48 being 64% ee (S) and 30% ee (R), respectively (entry l).60 7r-Allylpalladium intermediate 50 was proposed for this hydrosilylation. Use of phenyldifluorosilane in place of trichlorosilane slightly improved the enantioselectivity (entry 8).58,61 Similar level of enantioselectivity (71-72% ee) was reported for the reaction using Ar-MOP ligand 37f (entry 11) and its dioctylated derivative 37g (entry 12).57a... 

Early work involving simple alkenes employed the catalyst dichloro (y )-AUV-dimethyl-l-[(S)-2-(diphenylphosphino)ferrocenyl]ethylamine palladium(II), 1 (often abbreviated to Pd-Cl2[(i )-(S)-PPFA]). When applied to the hydrosilylation of norbornene with trichlorosilane, it yielded an adduct which was converted to a pentafluorosilicate and thence to the alcohol 2 in 25% overall yield and with 50% ee26. 

Improved results were achieved when trichlorosilane was treated with alkenes in the presence of a ferrocenyl-palladium catalyst, [(7 )-(5)-PPFA]PdCl2 8a. In the ease of unsymmetrica alkenes, Markovnikov addition products are formed. 

Asymmetric Hydrosilylation of Alkenes. The palladium complex PdCl2[(/ )-(5)-PPFA] catalyzes the asymmetric hydrosilylation of norbornene, styrene, and 1,3-dienes (eq 3). The hydrosilylation of 1-phenyl-1,3-butadiene with Trichlorosilane proceeds regioselectively in a 1,4-fashion to give (Z)-1-phenyl-1-silyl-2-butene of 64% ee. 

Palladium complexes [Pd(PPh3>4], [PdCl2(PPh3)2] and IPdCl2(PhCN)2] are not as reactive as H2PtCl6 toward hydrosilylation but they are more selective selective 1,4-addition to 1,3-dienes occurs to give aliylsilanes, and for asymmetric hydrosilylation with (R)-(S)-PPFA-Pd see Section 3.12.7. 

Hydrosilylation of monosubstituted alkenes with palladium catalysts and trichlorosilane follows a course which favors branched products. By using a chiral phosphine ligand, asymmetric reaction is feasible. Initially, menthyldiphenylphosphine (MDPP, 93) and neomenthyldiphenylphosphine (NMDPP, 94) were employed with little success. Later, (/ )-/VA -dimethyl-l-[(S)-2-diphenylphosphinoferroce-nyl]ethylamine [(R)-(S)-PPFA] (95) and its enantiomer were prepared, and these have proved to be the... 

The palladium/PPFA-catalyzed asymmetric cross-coupling of a-(trimethylsilyl)-benzylmagnesium bromide 25 has also been applied to the synthesis of optically active propargylsilane 29 (18% ee) by the use of l-bromo-2-phenylacetylene as a coupling partner (Scheme 2-18) [37]. 

The chiral ferrocenylmonophosphine ligand 7c, which is analogous to PPFA 3a but contains a perfluoroalkyl group on the aminoethyl side chain, is more enantioselective than PPFA (Scheme 2-48) [67]. The enantioselectivity in the palladium-catalyzed hydrosilylation of cyclopentadiene and 1-vinylcyclohexene is increased to 60% ee and 43% ee, respectively. The polymer-supported PPFA 62 has been used for the hydrosilylation of styrene (15% ee) [68]. 

Asymmetric synthesis through a selective monofunctionalization of enantiotop-ic positions is considered as being one of the most attractive strategies for the one-step construction of multiple chiral carbon centers [34,35]. Asymmetric hydrosilylation of norbornene (21) was first attempted by use of a palladium catalyst coordinated with ferrocenylmonophosphine, (1 )-(S)-PPFA (15a) [28]. The... 

Palladium-catalyzed hydrosilylation of 1,3-dienes is one of the important synthetic methods for allylic silanes, and considerable attention has been directed to the asymmetric synthesis of the latter by catalytic methods [9]. Optically active allyhc silanes have been used as chiral allylating reagents in S reactions with electrophiles, typically aldehydes [38,39]. In the presence of Pd catalysts the reaction with hydrosilanes containing electron-withdrawing atoms or substituents on sihcon usually proceeds in a 1,4-fashion giving allyHc silanes [40,41]. Asymmetric hydrosilylation of cyclopentadiene (29) forming optically active 3-silylcyclopentene (30) has been most extensively studied (Scheme 13). In the first report, hydrosilylation of cyclopentadiene (29) with methyldichlorosilane in the presence of 0.01 mol % of palladium-(l )-(S)-PPFA (15a) as a catalyst gave... 

It was found that the ferrocenylphosphines containing an (dialkylami-no)alkyl group on the side chain are effective for the cross-coupling of 2a catalyzed by nickel or palladium complexes [8, 9,10]. Ferrocenylmonophosphine, (S)-(iI)-PPFA (10a) and -bisphosphine, (S)-(i )-BPPFA (14) gave the coupling product 6 with 68% ee and 65% ee, respectively. The presence of the (dialkylami-no)alkyl side chain is of primary importance for the high selectivity and the enan-... 

The influence of the extent of conversion on enantioselectivity has been studied in the reaction of the Grignard reagent 2b with 4a catalyzed by the nickel complex of (S)-(1 )-BPPFA (14) [12]. A ferrocenylphosphine 16 which is analogous to PPFA but has a tetrahydroindenyl moiety was more enantioselective than PPFA (10a) for the palladium-catalyzed asymmetric cross-couphng of 2a with 4b to give (R)-6 of 79% ee [13] (entry 15). 

The asymmetric cross-coupling was successfully applied to the synthesis of optically active allylsilanes [50,51] (Scheme 10). The reactions of a-(trimethyl-silyl)benzylmagnesium bromide (49) with vinyl bromide (4b), (E)-bromopro-pene (( )-50), and (R)-bromostyrene E)-8) in the presence of 0.5 mol % of a palladium complex coordinated with chiral ferrocenylphosphine, (R)-(S)-PPFA (10a), gave the corresponding (R)-allylsilanes (51) with 95%, 85%, and 95% ee, respectively, which were substituted with phenyl group at the chiral carbon center bonded to the siHcon atom. These allylsilanes were used for the S. ... 

Dichloro((/ )-AA -dimethyl-l-[(S)-2-(diphenylphosphino)ferrocenyl]ethylamine) palladium(II), [(R)-(5)-PPFA]PdCl2, is an efficient catalyst for the asynunetric hydrosilylation of styrene and norbomadiene with HSiCl3, which gives rise to (S)-a-phenyl-ethyltrichlorosilane and (lR,25,45)-norbomyltrichlorosilane, respectively, in good yields ... 

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