The preparation of a crystalline, peracetyl adamantanyl thiosialoside donor protected by an isothiocyanate group is described. On activation at -78 C in the presence of typical carbohydrate acceptors this donor gives high yields of the corresponding sialosides with exquisite α-selectivity. The high selectivity extends to the 4-O-benzyl-protected 3-OH acceptors that are typically less reactive and selective than galactose 3,4-diols. Treatment of the α-sialosides with tris(trimethylsilyl)silane or allyltris(trimethylsilyl)silane sialosides replaces the C5-N5 bond by a C-H or a C-C bond. Reaction of the isothiocyanate-protected sialosides with thioacids achieves conversion into amides. Reaction of the isothiocyanate with an amine gives a thiourea, which can be converted to a guanidine. The very high α-selectivities observed with the new donor and the rich chemistry of the isothiocyante function considerably extend the scope for optimization at the sialoside 5-position.

A general and practical approach for the synthesis of C-4 chiral building blocks using Jacobsen's hydrolytic kinetic resolution technique to resolve terminal epoxides and diols in high enantiomeric excess and excellent yields is described. The utilization of these building blocks for the synthesis of biologically important natural products L-carnitine and a-lipoic acid is illustrated.

An N-acetyl oxazolidinthione protected sialyl thioglycoside was synthesized and its use as a sialyl donor studied. The strongly electron-withdrawing nature of the oxazolidinthione moiety is such that activation could not be achieved at −78 °C. Couplings were therefore conducted at the lowest convenient temperature (−50 °C). Glycosides were formed in good yield but in two out three cases studied selectivities were lower than those seen with the corresponding N-acetyl oxazoldinone protected donor. The resulting N-acetyl oxazolidinthione protectd disaccharides were converted to the corresponding N-acetyl oxazolidinones by treatment with N-iodosuccinimide and triflic acid in the presence of water at 0 °C.

The preparation of a crystalline, peracetyl adamantanyl thiosialoside donor protected by an isothiocyanate group is described. On activation at −78 °C in the presence of typical carbohydrate acceptors, this donor gives high yields of the corresponding sialosides with exquisite α‐selectivity. The high selectivity extends to the 4‐O‐benzyl‐protected 3‐OH acceptors, which are typically less reactive and selective than galactose 3,4‐diols. Treatment of the α‐sialosides with tris(trimethylsilyl)silane or allyltris(trimethylsilyl)silane results in replacement of the C5N5 bond by a CH or a CC bond. The reaction of the isothiocyanate‐protected sialosides with thioacids generates amides, while reaction with an amine gives a thiourea, which can be converted into a guanidine. The very high α‐selectivities observed with the new donor and the rich chemistry of the isothiocyante function considerably extend the scope for optimization at the sialoside 5‐position.

Vinylogie: Fortschritte in der asymmetrischen Katalyse mit difunktionellen Chinaalkaloiden/Harnstoffen ermöglichten eine Umpolung der klassischen Cβ‐Reaktivität von 3‐Alkylidenoxindolen. Damit gelang die Entwicklung des ersten und einzigen Beispiels einer direkten, organokatalytischen asymmetrischen vinylogen Michael(AVM)‐Reaktion mit Nitroolefinen.