'Hidden' axial chirality as a stereodirecting element in reactions involving enol(ate) intermediates. Part 2. Cyclisation reactions of methyl (4R)-3-(2-diazo-3-oxobutanoyl)-1,1-dioxo-1 lambda(6),3- (and 1-oxo-1 lambda(4),3-)thiazolidine-4-carboxylates

Methyl (4R)-3-(2-diazo-3-oxobutanoyl)-1,1-dioxo-1 lambda(6),3-thiazolidine- 4-carboxylate 14 undergoes a base-induced cyclisation to give methyl (8aS)- 3-acetyl-4,7,7-trioxo-1,4,6,7,8,8a-hexahydro-7 lambda(6)-[ 1,3]thiazolo[4,3 -c][ 1,2,4]triazine-8a-carboxylate 15 in a state of high enantiomeric purit y. Similar stereoselective cyclisations, proceeding with retention of confi guration, are observed with methyl (1R,4R)- and (1S,4R)-3-(2-diazo-3-oxobut anoyl)- 1-oxo-1 lambda(4),3-thiazolidine-4-carboxylates 25 and 27 to give c ompounds 33 and 34. It is suggested that the cyclisation reactions proceed by way of planar ester enol(ate) intermediates which possess axial chiralit y, e.g. 35. The bicyclic sulfone 15 and the bicyclic sulfoxides 33 and 34 are also prod uced by oxidation of methyl (8aS)-3-acetyl-4-oxo-1,4,8,8a-tetrahydro[1,3]th iazolo[4,3-c][1,2,4]triazine-8a-carboxylate 5 with m-chloroperoxybenzoic ac id (in DMF in the case of the sulfone 15 and in CHCl3 in the case of the:su lfoxides 33 and 34). The use of the oxidant in methanol or of hydrogen pero xide in formic acid leads to an oxidative deacetylation to give methyl (8aS )-3,4,7,7-tetraoxoperhydro-7 lambda(6)-[1,3]thiazolo[4,3-c][l,2,4]triazine- 8a-carboxylate 17, the structure of which is established by an X-ray crysta llographic analysis. The analysis reveals an interesting packing arrangemen t of the molecules in the crystal, attributable to an intermolecular I-I-bo nding network. In particular, intermolecular II-bonding between the ester c arbonyl oxygen atom and the amino hydrogen atom at position 1 provides a po ssible explanation for the shift of the ester carbonyl absorption to 1680 c m(-1) in the solid-state IR spectrum of compound 17.