α-Nitro Ketone as an Electrophile and Nucleophile: Synthesis of 3-Substituted 2-Nitromethylenetetrahydrothiophene and -tetrahydrofuran as Drosophila Nicotinic Receptor Probes

3-(6-Chloropyridin-3-yl)methyl-2-nitromethylenetetrahydrothiophene 2 and -tetrahydrofuran 3 were synthesized through novel approaches using alpha-nitro ketone intermediates as an electrophile and nucleophile, respectively. The 2-nitromethylenetetrahydrothiophene 2 was formed exclusively as the Z-isomer through intramolecular attack by a thiol substituent at the carbonyl group of an alpha-nitro ketone, in which the alpha-nitro ketone served as an electrophile. In contrast, the corresponding 2-nitromethylenetetrahydrofuran 3, not accessible by the above route due to limited stability, was prepared as a mixture of E- and Z-isomers by intramolecular attack of the alpha-nitro ketone enol anion in which the deprotonated alpha-nitro ketone served as a nucleophile. These compounds, together with the corresponding 2-nitromethylenepyrrolidine (1), were used to probe the Drosophila neonicotinoid-nicotinic acetylcholine receptor interaction.