Diketene 2-oxazolines

Other six-membered rings with two heteroatoms are also obtained from reaction of diketene with imidates, cyanamides, carbodiimides, isocyanates, oxazolines, or other multifunctional compounds. 

Very diverse routes have been followed in the preparation of perhydro-oxazolo[3,2-a]pyridines, particularly those incorporating amide functions. Systems of type 226 have been obtained by the reaction between substituted A -oxazolines with diketene (66FRPI441937) and of 228, from the oxazoline (227) with azidoketene (77MII). 

Besides the more often-used acyl donors mentioned above, others which would also ensure an irreversible type of reaction have been investigated [170]. Bearing in mind that most of the problems of irreversible enzymatic acyl transfer arise from the formation of unavoidable byproducts, emphasis has been put on finding acyl donors that possess cyclic structures, which would not liberate any byproducts at all. However, with candidates such as lactones, lactams, cyclic anhydrides (e.g., succinic acid anhydride [171]), enol lactones (e.g., diketene [172, 173]), and oxazolin-5-one derivatives [174], the drawbacks often outweighed their merits. 

Approaches to nucleoside synthesis by additions to suitably activated N-glycosides continue to receive attention. Ribofuranosyl purines have been prepared by addition of the imidazole derivative (7) to the glycosyl iminoether (8). Both a- and /3-ribosyl hypoxanthines and the corresponding 6-thio analogues were prepared in this manner. Addition of diketene to the amino-oxazoline derivative (9) gave a cyclonucleoside which was hydrolysed to the nucleoside analogue (10). Cyclization of ribopyranosyldiaminomaleonitrile... 

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