Synthesis and ring opening reactions of 2-glyco-1,4-dimethyl-3-nitro-7-oxabicyclo[2.2.1]hept-5-enes

Abstract

The high-pressure asymmetric Diels–Alder reactions of d- galacto- ( 1a) and d- manno-3,4,5,6,7-penta- O-acetyl-1,2-dideoxy-1-nitrohept-1-enitol ( 1b) with 2,5-dimethylfuran ( 2) afforded mixtures of cycloadducts, from which the (2 S,3 R)-3- exo-nitro ( 3a and 3b), (2 R,3 S)-3- exo-nitro ( 4a and 4b), and (2 R,3 S)-1′,2′,3′,4′,5′-penta- O-acetyl-1′- C-(1,4-dimethyl-3- endo-nitro-7-oxabicyclo[2.2.1]hept-5-en-2- exo-yl)- d- galacto-pentitol ( 5b) were isolated pure. Deacetylation of these compounds led to new chiral mono-, bi-, and tricyclic ethers, being their asymmetric centers arising from the chiral inductor used in the cycloaddition reaction. A ring opening mechanism through a 1-nitro-1,3-cyclohexadiene intermediate has been proposed.