Stereoselective synthesis, See

CsHizO, Mr 180.16, mp. 134-136 °C, [a]g -260° (HjO). A rare ketohexose epimer of sorbose from plant rubbers, especially of the tropical tree Sterculia setigera. T. can also be formed from " lactose in strongly heated milk. The synthesis proceeds, e.g., through oxidation of D-talitol by Acetobacter suboxy-dans. For stereoselective synthesis, see Ut.. ... 

This highly efficient DKR methodology was applied to the synthesis of the selective serotonin reuptake inhibitor, norsertraline (Scheme 1.4), which is used to treat depression. For the application of enzymatic dynamic kinetic resolution in stereoselective synthesis, see chapter 57. 

Total syntheses have been reported by E.J. Corey (1978B, 1979). We outline only the stereoselective synthesis of a protected fragment (A) which contains carbon atoms 1—9. This fragment was combined with fragment (B) by a Grignard reaction and cyclized by one of the methods typical for macrolide formation (see p. 146). 

An expedient and stereoselective synthesis of bicyclic ketone 30 exemplifies the utility and elegance of Corey s new catalytic system (see Scheme 8). Reaction of the (R)-tryptophan-derived oxazaboro-lidine 42 (5 mol %), 5-(benzyloxymethyl)-l,3-cyclopentadiene 26, and 2-bromoacrolein (43) at -78 °C in methylene chloride gives, after eight hours, diastereomeric adducts 44 in a yield of 83 % (95 5 exo.endo diastereoselectivity 96 4 enantioselectivity for the exo isomer). After reaction, the /V-tosyltryptophan can be recovered for reuse. The basic premise is that oxazaborolidine 42 induces the Diels-Alder reaction between intermediates 26 and 43 to proceed through a transition state geometry that maximizes attractive donor-acceptor interactions. Coordination of the dienophile at the face of boron that is cis to the 3-indolylmethyl substituent is thus favored.19d f Treatment of the 95 5 mixture of exo/endo diastereo-mers with 5 mol % aqueous AgNC>3 selectively converts the minor, but more reactive, endo aldehyde diastereomer into water-soluble... 

The carbonyl addition reactions of benzylmetals, compared to the allylic counterparts, have found few applications in stereoselective synthesis, apparently for the following reasons The carbonyl addition of alkali metal salts (M = Li, Na, K, Cs) of benzyl anions, with few exceptions, usually proceeds with low levels of simple diastereoselectivity affording mixtures of syn- or <7 / -diastereomers (see Section 1.3.2.3.1.). 

The enzyme-catalyzed stereoselective synthesis of (/ )- and (S )-cyanohydrins allows a simple access to compounds which can be easily transformed into the corresponding a-hydroxy-car-boxylic acids (see Table 2)20,21,23, a-hydroxyaldehydes26 or acyloins27, without racemization. 

Based on the facile formation and reactivity of323, and the retro Diels-Alder reaction of 325306,310, a simple procedure has been developed for the stereoselective synthesis of functionalized conjugated dienes as well as vinylallenes311 (see equation 119). 

There can be significant differences in the rates of elimination of the stereoiso-meric (3-hydroxysilanes. Van Vranken and co-workers took advantage of such a situation to achieve a highly stereoselective synthesis of a styryl terpene. (The lithiated reactant is prepared by reductive lithiation see p. 625). The syn adduct decomposes rapidly at -78° C but because of steric effects, the anti isomer remains unreacted. Acidification then promotes anti elimination to the desired /i-isomer.275... 

There is little doubt that the hydrogenation of dehydro a-amino acids is the best-studied enantioselective catalytic reaction. This was initiated by the successful development of the L-dopa process by Knowles (see below) and for many years, acetylated aminocinnamic acid derivatives were the model substrates to test most newly developed ligands. As can be seen below, this is the transformation most often used for the stereoselective synthesis of a variety of pharma and... 

For further examples of the stereoselective synthesis of ring systems, see anodically initiated cycloadditions in Sect. 13.4.2.1.3. 

It has been established that the course of the sequential pericyclic reaction of cyclopentadienones with acyclic conjugated alkadienes depends on the reaction temperature, thermal treatment at low temperatures affording 3a,4,7,7a-tetrahydroinden-l-one derivatives by way of a Cope rearrangement (see Scheme 38). Roman et al have developed an efficient stereoselective synthesis of enantiomerically pure i-nitrotricyclo[5.2.2.0 ]undeca-3,8-dienes via a tandem consecutive asymmetric Diels-Alder-Cope rearrangement (see Scheme 39). Adducts... 

A short stereoselective synthesis of the pentacyclic key intermediate (179) in Ireland s syntheses of friedelin and alnusenone (see Vol. 7, p. 149) is outlined in Scheme 5. ... 

Vasella has applied the concept of anomeric anion stabilization by a nitro group to the /3-D-JV-acetyl-D-glucosamine derivative 177, available in four steps from N-acetyl-n-glucosamine [52] (Scheme 39). Reaction of the tetraethylammonium nitronate derived from 177 with aldehyde 178 provides anti-179 which then undergoes stereoselectively reduction (see Sect. 2.2.1) to provide -C-glycoside 180, intermediate in a synthesis of N-acetyl-neuraminic acid. 

For another example of stereoselective synthesis with chiral crowns see Section 5.2.I.5.I. 

Tor a treatise on this subject, sec Morrison Asymmetric Synthesis, 5 vols. [vol. 4 co-cditcd by Scott] Academic Press New York, 1983-1985. For books, see N6gr4di Stereoselective Synthesis VCH New York, 1986 Eliel Olsuka Asymmetric Reactions and Processes in Chemistry American Chemical Society Washington, 1982 Morrison Mosher Asymmetric Organic Reactions Prentice-Hall Englewood Cliffs, NJ, 1971, paperback reprint, American Chemical Society Washington, 1976 Izumi Tai, Ref. I. For reviews, see Ward Chem. Soc. Rev. 1990, 19, 1-19 Whitesell Chem. Rev. 1989, 89, 1581-1590 Fujita Nagao Adv. Heterocycl. Chem. 1989, 45, 1-36 Kochetkov Belikov Russ. Chem. Rev. 1987, 56, 1045-1067 Oppolzer Tetrahedron 1987, 43, 1969-2004 Seebach Imwinkelried Weber Mod. Synth. Methods 1986, 4, 125-259 ApSimon Collier Tetrahedron 1986, 42, 5157-5254 Mukaiyama Asami Top. Curr. Chem. 1985, 127, 133-167 Martens Top. Curr. Chem. 1984, 125, 165-246 Duhamel Duhamel Launay Plaqucvcnt Bull. Soc.Chim. Fr. 1984,11-421-11-430 Mosher Morrison Science 1983,221, 1013-1019 Schollkopf Top. Curr. Chem. 

For reviews of stereoselective alkylation of enolates, see Ndgrtidi Stereoselective Synthesis, VCH New York, 1986, pp. 236-245 Evans, in Morrison Asymmetric Synthesis, voi. 3 Academic Press New York, 1984, pp. 1-110. Hughes Dolling Ryan Schoenewaldt Grabowski 7. Org. Chem. 1987, 52, 4745. 

For reviews of the stereochemistry and mechanism, see Caro Boyer Lamaty Jaoucn Bull. Soc. Chim. Fr. 1983,11-281-1T303 Boone Ashby Top. Siereochem. 1979, II, 53-95 Wigfield Tetrahedron 1979, 35, 449-462. For a review of stereoselective synthesis of amino alcohols by this method, see Tramontini Synthesis 1982, 605-644. 

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