A Diop, as ligand

Simple esters cannot be allylated with allyl acetates, but the Schiff base 109 derived from o -amino acid esters such as glycine or alanine is allylated with allyl acetate. In this way. the o-allyl-a-amino acid 110 can be prepared after hydrolysis[34]. The Q-allyl-o-aminophosphonate 112 is prepared by allylation of the Schiff base 111 of diethyl aminomethylphosphonates. [35,36]. Asymmetric synthesis in this reaction using the (+ )-A, jV-dicyclohex-ylsulfamoylisobornyl alcohol ester of glycine and DIOP as a chiral ligand achieved 99% ec[72]. 

The majority of studies of asymmetric hydroformylation with rhodium and platinum complexes have made use of DIOP (49) as a ligand. With either the complex [RhCl(CO)(DIOP)] or [RhCl(C2H4)2]2 plus DIOP, styrene was hydroformylated to 2-phenylpropanal with optical yields of only 16%.366 When a-monodeuterostyrene was used as substrate, with DIOP and complex (34) as catalyst, essentially the same optical yield was obtained.367 The same catalyst with non-deuterated styrene under different conditions gave an optical yield of 25%.368... 

The reduction of lactam substrates containing proximal exo double bonds may be achieved in high e.e. as demonstrated by the reduction of 3-alkylidene-2-piperidones (Scheme 19)119. Cyclic amino acids may be prepared by, for example, asymmetric hydrogenation of 3 to 4 in up to 79% e.e.120 and the reduction of 5 to 6 in 99% e.e.121. In the latter case a number of chiral diphosphines were screened, and the best results were obtained using BINAP as a ligand with rhodium metal. Several other diphosphines, notably DuPHOS and DIOP, also performed well. The research group which produced... 

It is well-established that either 3-pentenoate or 3,8-nonadienoate are obtained by the carbonylation of butadiene depending on the nature of the catalysts. So far no successful asymmetric carbonylation of prochiral dienes is known. Alper carried out enantioselective thiocarbonylation of prochiral dienes, such as 2-methyl-l,3-pentadiene (30), with thiophenol and obtained the, y-unsaturated thioester 31 with 89 % ee in 71 % yield using (/ , / )-DIOP as a chiral ligand [9]. 

Directed and Asymmetric Reduction The principles of directed and asymmetric reactions were first developed for hydrogenation, as discussed in Section 9.2. Asymmetric hydrosilation of ketones can now be carried out cata-lytically with rhodium complexes of diop (9.22). The new chiral ligand Et-duPHOS, made by Burk at du Pont, allows chiral amination of ketones via Eq. 14.50. Note how the use of the hydrazone generates an amide carbonyl to act as a ligand, as is known to favor high e.e. (see Section 9.2). Noyori s powerful BINAP ligand has been applied to a large number of asymmetric reactions. 

The addition of sulfonyl chlorides to alkenes In the presence of a catalytic amount of dIchlorotris(triphenylphosphIne) ruthenlum(II) affords 1 1 adducts. Under these reaction conditions It Is believed that sulfonyl radicals, which are confined to the coordination sphere of the metal complex, are involved. When the chiral phosphine (—)-DIOP ((2,3-0-isopropylidene)-2,3-dihydroxy-l,4-bis(diphenylphosphino)butane) is used as a ligand, the addition of 4-methoxybenzenesulfonyl chloride to styrene proceeds to provide the (R) isomer in 40% ee (eq 2). ... 

The palladium(ii) acetylacetonate-tri phenyl phosphine catalysed reaction of butadiene with water and carbon dioxide in solvents such as t-butanol or acetone has been reported to give octa-2,7-dien-l-ol as the major product together with minor amounts of octa-l,7-dien-3-ol, 1,3,7-octatriene and octadienyl ethers. In contrast aqueous potassium tetrachloropalladate with excess diene leads to pale yellow solids which were polymeric. Decomposition of these complexes with dimethylglyoxime gave a mixture of 3-methyIbutenyl ethers, (Scheme 33). The use of (—)-2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-l,3-dioxolane (DIOP) as a chiral ligand... 

Early work in the field of asymmetric hydroboration employed norbornene as a simple unsaturated substrate. A range of chiral-chelating phosphine ligands were probed (DIOP (5), 2,2 -bis(diphenyl-phosphino)-l,l -binaphthyl (BINAP) (6), 2,3-bis(diphenylphosphino)butane (CHIRAPHOS) (7), 2,4-bis(diphenylphosphino)pentane (BDPP) (8), and l,2-(bis(o-methoxyphenyl)(phenyl)phos-phino)ethane) (DIPAMP) (9)) in combination with [Rh(COD)Cl]2 and catecholborane at room temperature (Scheme 8).45 General observations were that enantioselectivities increased as the temperature was lowered below ambient, but that variations of solvent (THF, benzene, or toluene) had little impact. 

A breakthrough in this area came when Dang and Kagan3 synthesized DIOP, a C2 chiral diphosphine obtained from tartaric acid (Fig. 6-1). DIOP-Rh(I) complex catalyzed the enantioselective hydrogenation of a-(acylamino)acrylic acids and esters to produce the corresponding amino acid derivatives with up to 80% ee. These achievements stimulated research on a variety of bidentate chiral diphosphines, and numerous chiral ligands bearing C2 symmetry have been developed as a result (see Fig. 6-1 for examples). 

Using (/ ,/ )-Diop as the chiral auxiliary, the amount of chiral induction is not dependent on the temperature, but depends on the type of chiral ligand in the palladium complex and on the allenylmetal reagent. When magnesium or copper is present, a reversal of the configuration... 

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