Palladium and boron co-catalyzed addition of oxygen...

Details Palladium and boron co-catalyzed addition of oxygen... Palladium and boron co-catalyzed addition of oxygen...

1999-09-07

2001-10-23

Keys, Rosalynd (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C549S378000, C549S346000, C549S427000, C549S497000, C564S487000, C564S413000, C568S675000, C568S662000, C568S857000

Reexamination Certificate

active

06307067

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a catalytic method for use in highly regioselective and enantioselective additions of oxygen nucleophiles to vinyl epoxide substrates. The reaction employs a chiral Pd complex and a boron co-catalyst. Also described are additions of nitrogen nucleophiles, and related addition reactions of oxygen nucleophiles employing only the chiral Pd catalyst.
REFERENCES
Boudreau, C. et al., U.S. Pat. No. 5,574,186(1996).
Bunt, R. C., Ph.D. Thesis, Stanford University, 1996, p. 252.
Collman, J. P. et al., Science 26:1404 (1993).
Guibe, F., Saint M'Leux, Tetrahedron Leu. 1981, 22, 3591.
Jacobsen, E. N. et al., J. Am. Chem. Soc. 112:2801 (1990).
Jacobsen, E. N. et al., Science 277(5328):936-938 (1997a).
Jacobsen, E. N. et al., U.S. Pat. No. 5,665,890 (1997b).
Katsuki, T. and Sharpless, K. B., U.S. Pat. No. 4,471,130 (1984).
Lakamiri, R., Lhoste, P., and Sinou, D,. Tetrahedron Lett. 1989, 30, 4669.
Lakhmiri, R., Lhoste, P., and Sinou, D., Synth. Commun. 1990a, 20, 1551.
Lakhmiri, R., Lhoste, P., Boullanger, P., and Sinou, D., J. Chem. Res. (S), 1990b, 342.
Saigo, K. et al., Bull. Chem. Soc. Japan 59(3):931 (1986).
Singaram, B. et al., U.S. Pat. No. 5,367,073 (1994).
Sinou, D. et al., Tetrahedron Lett. 1995, 36, 251.
Trost, B. M. and Tenaglia, A., Tetrahedron Len. 1988, 29, 2931.
Trost, B. M., Ito, N., and Greenspan, P. D., Tetrahedron Lett. 1993, 34, 1421.
Ukai, T. et al., J. Organometal. Chem 1974, 65, 253.
BACKGROUND OF THE INVENTION
A long-standing challenge in palladiumn &pgr;-allyl chemistry has been the use of oxygen nucleophiles to generate O-allylated species with good regio- and enantioselectivity (FIG.
1
A). Although phenols and carboxylates have been shown to be good nucleophilic partners for this type of reaction, alcohols have generally given poor results due to their sluggish reactivity and moderate regioselectivity.
Only a few literature examples employing alcohols as nucleophiles with Pd &pgr;-allyls have appeared, most of which involve simple O-allylation of alcohols (Lakhmiri et al., 1989), in which neither regio- nor stereoselectivity is an issue (Guibe et al, Lakhmiri et al., 1990
a,
1990
b
). Several examples of Pd(0)-catalyzed O-glycosylation of sugars to produce 1,4-disaccharides have been reported by Sinou et al.
Trost et al have investigated a number of strategies for the delivery of oxygen nucleophiles (or hydroxyl equivalents) to Pd &pgr;-allyl complexes arising from vinyl epoxides. Specifically, Trost and Tenaglia (1988) examined the use of alkoxystannanes for the regioselective 1,2-addition of alkoxy groups to vinyl epoxides. The reaction was not stereoselective, and its scope of this reaction was somewhat limited in that good yields were obtained only by the use of cyclic stannylene diethers.
As part of a total synthesis of zoapatanol, Trost and Ito (1993) developed the use of triphenylsilanol as a water surrogate that selectively adds in a 1,4sense to vinyl epoxides. The products of this reaction were formed mainly with the E-geometry. However, attempts to repeat this work using a chiral ligand (Bunt, 1996) were unsuccessful.
A general method for regio- and enantioselective addition of alcohols to vinyl epoxides, therefore, has not yet been reported. Such a procedure would be extremely valuable in the preparation of chiral precursor molecules to biologically important molecules, or as building blocks for chiral reagents for use in synthesis, optical resolution, etc. In particular, the enantioselective addition of a hydroxyl equivalent (more precisely, a water equivalent) to a vinyl epoxide would generate the vinylglycidol in enantiopure form. The latter chemistry would provide a facile route to two commercially important chiral pool molecules and, as such, would be competitive with the Jacobsen procedure (i.e. kinetic resolution of the corresponding epoxides; Jacobsen, 1997
a
) for generation of these materials.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a method of selectively adding a nucleophilic species, preferably a nucleophilic oxygen species, to a vinylic epoxide. The vinylic epoxide is contacted with a borane or borate reagent, in the presence of said nucleophilic species and a chiral catalytic Pd complex, thereby forming an addition product, preferably an O-allyl product, which is enriched in one of the possible stereoisomeric products of such an addition. The nucleophilic oxygen species is preferably a primary alcohol, water, an acetate, a carbonate, or a bicarbonate.
In a preferred procedure for carrying out the reaction, the nucleophilic species and chiral catalytic Pd complex are combined, prior to or concomitant with contacting the vinylic epoxide and boron reagent, in a substantially oxygen-free atmosphere in a solvent selected from dichloromethane, 1,2-dichloroethane, tetrahydrofuran, and diethyl ether. Dichloromethane is a particularly preferred solvent. The concentration of the vinylic epoxide in the reaction mixture is preferably less than 1.0M, more preferably less than 0.5M, and most preferably about 0.1 to 0.25M, although lower concentrations may be used.
The borane or borate reagent preferably comprises boron substituted with three groups independently selected from alkyl, alkoxy, aryl, aryloxy, aralkyl, aralkyloxy, alkylamino, arylamino, aralkyl, aralkylamino, hydroxy, or oxide. Preferred species are trialkylboranes, dialkylalkoxyboranes, dialkoxyalkylboranes, or trialkyl borates, where the alkyl or alkoxy substituents may be further substituted with aryl. Particularly preferred are those represented by BR
3
, BR
2
OR′, BR(OR′)
2
, or B(OR)
3
, where R and R′ are independently C
1
to C
4
alkyl or benzyl. Of these, preferred compounds are Et
3
B, s-Bu
3
B, n-Bu
3
B, Et
2
BOMe, B(OiPr)
3
, B(OtBu)
3
, and B(OBz)
3
.
The chiral catalytic Pd complex is typically formed in situ from (i) a Pd(0) species, or a Pd(II) species effective to be reduced to a Pd(0) species, and (ii) a chiral ligand effective to form the complex by reaction with the Pd(0) species. The chiral catalytic Pd complex includes a chiral ligand, where the ligand preferably comprises (i) a chiral component derived from a chiral diamine, diol, amino alcohol, or dicarboxylic acid, this component having first and second chiral centers, each substituted with a group X selected from oxygen, nitrogen, or a carbonyl group, and, (ii) linked to each group X, a binding component, comprising a sterically bulky group effective to complex with the central palladium atom. Preferably, this group is a phosphine-containing group, and most preferably a (diarylphosphino)aryl group, such as 2-(diphenylphosphino)benzene or 2-(diphenylphosphino) naphthalene. In preferred ligands, each of the binding components, which need not be identical, is linked to a chiral center of the chiral component via a carboxylic amide or carboxylic ester linkage.
The chiral centers are connected by a direct bond, or by a chain of one to three atoms comprising linkages selected from alkyl, alkenyl, ailyl ether, alkyl amino, or a combination thereof. Preferably, the chiral component is derived from a chiral diamine, and more preferably a chiral 1,2-diamine, such as enantiomerically enriched trans-1,2-cyclohexyldiamine, trans-1,2-diamino-1,2-diphenylethane, or dibenzo-2,3-diamino[2.2.2]bicyclooctane. In particularly preferred ligands, a (diarylphosphino)aryl group, such as those named above, is linked to a chiral center of said chiral component via a 1-amido linkage.
In a preferred embodiment of the method, the vinylic epoxide is a terminal epoxide, having no further substitution at the epoxy carbons, such as butadiene monoepoxide.
In one aspect, the addition is regioselective, in that the nucleophilic species adds predominantly at the epoxy carbon of said epoxide bearing the vinylic group, giving predominantly a 1,2-addition product. Preferably, no significant amount of the 1,4-addition product is produced. The addition is also enantioselective, and produces an addition product having an enantiomeric excess pre

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