Synthesis and structural study of 5-nitro-6-(penta- O-acetylpentitol-1-yl)norbornenes

Abstract

Uncatalyzed reaction between cyclopentadiene and ( E)-3,4,5,6,7-pentaacetoxy-1-nitrohept-1-enes having the d- manno, d- galacto, and d- gluco configurations at C-3—C-7 led, in each case, to the four stereoisomeric 5-nitro-6-(1,2,3,4,5-penta- O-acetylpentitol-1-yl)bicyclo[2.2.1]hept-2-enes. Face selectivity is discussed in terms of the sugar-chain configuration. The structures assigned the adducts are based on their n.m.r. spectra, and, in the case of the d- manno compounds, on X-ray data. Also described are the 13C-n.m.r. spectra of the starting nitroalkenes. The crystal structures of (5 S,6 S)1,2,3,4,5-penta- O-acetyl-1- C-(5- exo-nitrobicyclo[2.2.1]hept-2-en-6- endo-yl- d- manno-pentitol ( 3a) and (5 S,6 S)1,2,3,4,5-penta- O-acetyl-1- C-(5- endo-nitrobicyclo[2.2.1]hept-2-en-6- exo-yl- d- manno-pentitol ( 5a) were determined from three-dimensional, X-ray data. Crystals of 3a are monoclinic, space group P2 1, with two molecules in a cell of dimensions a = 9.054(3), b = 15.580(11), c = 10.138(4) Å, β = 116.27(3)°. The structure was refined to an R-factor of 0.050 on the basis of 1485 observations. Crystals of 5a are triclinic, space group P1, with one molecule in a cell of dimensions a = 8.680(4), b = 9.760(4), c = 8.695(7) Å, α = 98.69(5), β = 103.13(5), γ = 112.09(3)°. The structure was refined to an R-factor of 0.074 based on 970 observations.