ORGANIC SPECTROSCOPY INTERNATIONAL: 3,3-Dicarbethoxy-3,4-dihydro-9-(1-methylethylidene)-1,4-methano-1H-2-benzopyran

3,3-Dicarbethoxy-3,4-dihydro-9-(1-methylethylidene)-1,4-methano-1H-2-benzopyran
37

3,6-Di(2-pyridyl)stetrazine (0.45g; 1.9 mmol) was added slowly to a stirred solution of the hydrocarbon 33 (0.30g; 1.6 mmol) and diethyl oxomalonate 36(0.25 ml); 1.6 mmol) in chloroform (10 ml) and the resulting solution stirred for 1 hour. Removal of the solvent afforded the crude product. Attempts to purify this product by chromatography on silica gel or alumina only resulted in its rearrangement. However, the p.m.r. spectrum (CDCl₃) of the product could be deduced from that of the crude compound: d 1.02 (3H, t J = 7 Hz, endo-OCH2CH3), 1.30 (3H, t J = 7 Hz), exo-OCH2CH3), 1.72 (3H, s, methyl protons), 1.76 (3H, s, methyl protons), 3.96 (2H, q J = 7 Hz, endo-OCH2CH3), 4.36 (2H, q J = 7 Hz, exo-OCH2CH3), 4.74 (1H, d Ja,b = 1.5 Hz, Hb) 5.76 (1H, d Ja,b = 1.5 Hz, Ha), 7.10-7.60 (4H, m, aromatic protons), and the mass spectrum showed the parent ion at m/e 330.