Glycals activated

Nitro-activated glycals and aromatic compounds are good acceptors for TMM-Pd chemistry. The nitroglycal (19) reacts with (1) to give a 2.4 1 ratio of products (20) and (21) in a combined yield of 69% (Eq. 2). Treatment of the less electron-rich... 

Reaction of AcOF with glycals has been developed. Rozen and coworkers observed that elemental fluorine, which is practically insoluble in, and non-reactive with, acetic acid, gives rise to the active species, AcOF,... 

Little used organic acceptors for these reactions, also [53,54], The use of a glycal as the radical source together with a functionalized enone as the radical acceptor is remarkable. Enones are swiftly reduced by Cp2TiCT [55] and thus epoxide activation must be considered as even more efficient. The product of the addition constitutes a valuable intermediate en route to derivatives of thyrsiferiol. 

A refined version of this reaction was used to obtain opticaliy active 3 from glycal 2. This product is readily converted to the tetrahydropyran 4, a subunit of the antibiotic indanomycin. 

Scheme 3 Access to C-l glycals by C-l lithiation of C-2 activated glycols.

The method was first applied to the preparation of a number of simple alkyl and aryl C-l glycals,71 but since then the scope of this approach have been extended with the preparation of a small library of significant C-l glycals including steroidal, and glycerolipidic residues endowed with potential biological activity.72... 

The polymer bound thioethyl 2-amido glucosyl 51a is a competent 2-amidoglucosyl donor toward glycal acceptors when activated with methyl triflate in the standard manner.21 The formation of P-2-aminoglucosyl C1 —>4 53) and p-2-aminoglucosyl (1—>3 54)-linked disaccharides proceeded in over 70% yield (Scheme 2.16). The P-2-aminoglucosyl (1 —>6)-linked disaccharide 52 was formed in lower yields. 

Fucosyl phosphate 36 also very efficiently glycosylated the C4 position of acceptor 32. The orthogonality of the activating conditions of thioglycosides and glycosyl phosphate donors was exploited in the synthesis of trisaccharide glycal 41 (Scheme 6.7A).32 Furthermore, the different reactivity of a- and p-glycosyl phosphates was... 

The galactosyl glycal 72 was bound to solid phase via a silyl ether linker. Epoxidation of the glycal using 2,2-dimethyldioxirane and subsequent electrophilic activation of the epoxide resulted in the glycosylation of 3,4-di-O-benzyl glucal 73. After acetylation of the product, the polymer-linked trisaccharide 74 was obtained. 

In a total synthesis of (-)-laulimalide (288), Nelson et al. were able to assemble rapidly the bottom synthon of the target by adding carboalkoxyallenylstannane 286 to glycal 285 [60]. The Lewis acid activator Bu3SnOTf gave the best results, affording the anti SN2 addition product in 80% yield (Scheme 19.51). 

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