Formation and X-ray analysis of an aza-dihydrotriquinacene derivative from 4-cyano-1-methyl-1,2-dihydropyridine

Abstract

4-Cyano-1-methyl-1,2-dihydropyridine 1 is a highly activated captodative diene known to cyclodimerize, even at –45°C, in a [2 + 2] mode to 2 which isomerizes above –20°C to the [4 + 2] dimer 3. Compound 3 is now found to equilibrate above ∼50°C with the monomer 1. In addition 3 furnishes, with dimethyl acetylenedicarboxylate in boiling acetone, the expected [2 + 2] adduct 7 along with the title compound, a surprising 2 : 1 adduct 6 of dimethyl acetylenedicarboxylate and 1. Both new structures 6 and 7 are proven by X-ray analysis.

The crystals of 6(C₁₉H₂₀N₂O₈) are monoclinic, space group P2₁/n, Z= 4, with a= 13.818(2), b= 10.994(2), c= 13.128(2)Å, β= 100.09(1)°, V= 1963.4(5)ų. Using 2754 independent reflections with I 2.5σ(I) the structure was refined to R= 0.054. The crystals of 7(C₂₀H₂₂N₄O₄) are also monoclinic, space group P2₁/c, Z= 8, with a= 20.229(7), b= 11.307(3), c= 18.199(4)Å, β= 103.73(2)°, V= 4044(2)ų. This second structure was refined to R= 0.058 using 2718 observed reflections.