Oxidation and elimination reactions study in a formal synthesis of (±)-forskolin

Unusual C-C bond cleavage of an α-trifloxy Sialic acid hemiacetal under Lattrell-Dax conditions

We describe the novel oxidative fragmentation of methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-5-deoxy-3-O-trifluoromethanesulfonyl-β-D-erythro-L-gluco-2-nonulopyranos)onate 2 on stirring with sodium nitrite in DMF to give the novel 3-acetamido-2,5,6,7-tetra-O-acetyl-d-glycero-d-galacto-heptono-1,4-lactone 3 in excellent yield. Stirring of the same triflate with sodium carbonate on the other hand affords the novel methyl (5-acetamido-7,8,9-tri-O-acetyl-3,6-anhydro-5-deoxy-d-manno-3-ene-2-nonulos)onate 19 also in excellent yield. Reduction of the heptono lactone with sodium borohydride followed by acetylation gives a peracetylated aminodeoxyheptitol 6 that adopts the zig zag conformation of its carbon backbone.