Steric effects on rates and equilibria of a cation-anion combination reaction: the methoxide attachment to 4-substituted 2,6-di-tert-butylpyrylium cations (original) (raw)

1988, The Journal of Organic Chemistry

15). To 0.229 g (0.747 mmol) of 13 in 8 mL of dry pyridine was added 1.33 g (2.99 mmol) of lead tetraacetate. The mixture was placed in an oil bath at 75 "C until carbon dioxide evolution ceased. The solution was rotary evaporated and chromatographed on alumina with 0% MeOH in CHC1, and then on silica gel with 3% MeOH in CHCl,, yielding 0.0645 g (40%) of 15: 31P NMR (CDCl,) 8 +40.5; 13C NMR (CDCl,) 6 25.8 ( J = 108.8 Hz, C-3), Hz, C-meta), 129.1 (J = 8.8 Hz, C-6 or C-7), 129.2 (J = 4.4, C-6 or C-7), 131.6 ( J = 3.3 Hz, C-para), 131.7 ( J = 8.8 Hz, C-ortho), 132.5 ( J = 94.5 Hz, C-ipso), 134.8 (J = 22.0 Hz, C-5 or C-8),135.9 ( J = 19.8 Hz, C-5 or C-8); 'H NMR (CDCl,, 300 MHz) 6 1.70 (m, 1 H, unresolved d oft, CHH), 2.0 (m, 1 H, unresolved d of d, CHH), 4.10 (m, 2 H, H-1 and H-4), 6.18 (m, 1 H, olefinic H), 6.45 (m, 1 H, olefinic H), 6.65 (m, 2 H, olefinic H), 7.3-7.9 (Ar H); MS, mlz 216.0702 (M' , C13H130P; calcd 216.0704). Dimethyl 2-syn -Phenyl-2-phosphabicyclo[ 2.2.21oct-5ene-7,8-dicarboxylate (16). To a solution of 0.559 g (0.0041 mol) of trichlorosilane in 50 mL of dry benzene was added 0.9775 g (0.0123 mol) of dry pyridine in 10 mL of dry benzene. A solution of 0.25 g (0.00 75 mol) of 12 in 5 mL of dry benzene was added.