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.
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