Diastereoselectivity formation

Scheme 2.68. Diastereoselective formation of substituted tetrahydropyran-4-ones.

DIASTEREOSELECTIVE FORMATION OF TRANS-1,2-DISUBSTITUTED CYCLOHEXANES FROM ALKYLIDENEMALONATES BY AN INTRAMOLECULAR ENE REACTION DIMETHYL (1 R,2 R,5 R)-2-(2 -ISOPROPENYL-5 -METHYLCYCLOHEX-1 -YL)-PROPANE-1,3-DIOATE... 

Intramolecular cycloaddition of nitrile oxides, prepared from 1,2-isopropy-lidene-protected ether-linked oligo-pentoses leads to the diastereoselective formation of chiral isoxazolines fused to 10-16-membered oxa-cycles (456). 

Scheme 11.17 Diastereoselective formation of a tetrahydrofuran nucleus via 5-exo-trig alkyl radical cyclization on to an allene functionality in the course of a total synthesis of (+)-samin (56) [75], a)33 67 mixture of diastereomers.

The diastereoselective formation of dienol tricarbonyliron complexes on treating rf-2,4-pentadienal)Fe(CO)3 with functionalized zinc-copper reagents has been investigated (equation 49)66. Cyano-substituted complexes undergo intramolecular nucleophilic additions when treated with lithium diisopropylamide (LDA) as shown in equation 50. 

Scheme 3.7. Diastereoselective formation of /S-silyl ( )- or (Z)-ester enolates by silylcuprate conjugate addition followed by alkylation with aldehydes [49]. Stereoselective synthesis of ( )-and (Z)-allyl silanes [50].

Witt, D. Lagona, J. Damkaci, F Fettinger, J. C. Isaacs, L. Diastereoselective formation of methylene-bridged glycoluril dimers. Org. Lett. 2000, 2,755-758. 

Using (-)-lOO [46] as a chiral auxiliary tethered to the enolether, one face of the alkene can be specifically blocked by a n-n interaction of the phenyl rest for the [2 r5+2 r ] cycloaddition with a ketene [47], resulting in the highly diastereoselective formation of the cyclobutanone 102 (Scheme 15). The observed regio- and stereoselectivity is in accord with the stereochemical predictions made on the basis of the Woodward-Hoffmann... 

Chiral aziridines having the chiral moiety attached to the nitrogen atom have also been applied for diastereoselective formation of optically active pyrrolidine derivatives. In the first example, aziridines were used as precursors for azomethine ylides (90-95). Photolysis of the aziridine 57 produced the azomethine ylide 58, which was found to add smoothly to methyl acrylate (Scheme 12.20) (91,93-95). The 1,3-dipolar cycloaddition proceeded with little or no de, but this was not surprising, as the chiral center in 58 is somewhat remote from the reacting centers... 

Treatment of the alkenyl bromides 210 with tributyltin hydride in the presence of AIBN involves an intramolecular radical addition to the 2(3/f)-oxazolone moiety, resulting in the diastereoselective formation of the oxazolidinopiperidines 211. These are readily converted to the protected 2,6-disubstituted 3-hydroxypiperidine derivatives 212 (Fig. 5.51). ... 

An alternative approach to the PQQ-triester 130, a precursor to the cofactor PQQ, was developed starting with diethyl 4-oxopent-2-ynedioate 128 <1996HCA658>. Diastereoselective formation of diethyl (Z)-2-(2-(ethoxycarbonyl)-5-methoxy-l/7-indol-6-ylamino)-4-oxopent-2-enedioate 129 followed by acid-catalyzed cyclocondensation gave the target 130 (Scheme 19). 

Scheme 2.2.5.15 Highly diastereoselective formation of a bicyclic decadiulose from racemic tartaric dialdehyde by bidirectional chain extension.

TABLE 8. Representative examples of the diastereoselective formation of aldehydes and amines (equation 27)... 

The carbon skeleton of natural product galanthamine was prepared by the ring closure of an enantiopure aryl-cyclohexenyl ether. The transformation, run in the presence of a palladium-dppp catalyst and silver carbonate, led to the diastereoselective formation of the tricyclic product (3.25.). It is worth mentioning, that the chiral information in the ether intermediate was introduced in the palladium catalysed Tsuji-Trost reaction (N.B. the synthetic approach depicted in 3.13. and 3.25. are much alike).31... 

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