Comparison of two initiators of cyclisation derived from cyclohexen-1-ones

Abstract

The use of the enol trifluoroacetates of cyclohex-2-en-l-ones for initiating alkene cyclisation is compared with results from cyclisation of the related 2,3-epoxycyclohexanones.HARDING'S demonstration1 that protonation of cyclohexadienol acetates provided efficient initiating cations for monocyclisations prompted us to t r y this route where our Lewis acid-epoxide-induced cyclisations had given poor results., The success of dienol trifluoroacetate in our hands and, independently, in Harding's3 prompted us to make a more extensive comparison of the alternative methods. Compounds (3), ( 5 ) , and (6) gave comparable results in both types of cyclisation. Reaction of (3) with (CF,CO),O-CF,-C0,H at 0 "C gave, after hydrolysis, the cisand tramisomers? of (8) (56%) as an inseparable 2 : 1 mixture [7 (CDCl,) 2.8-3.5 (3H, m), 8.66 ( s ) , and 8.94 (s)] while the 2,3-epoxide with SnC1,-CH,Cl, a t -20 OC, gave the related /3-hydroxy compound in 88% yield [vmax 1710 cm-1;

1,3-Benzodithiolium cation mediated cyclization reactions

“…These extracts were combined, washed with saturated aqueous sodium chloride solution (2 X 20 mL), and dried (MgS04). The solvent was removed in vacuo, and the resultant yellow residue was isolated via flash column chromatography (10% THF/hexane) to give 0.316 g (93%) of a viscous yellow oil: IR (CC14) p 3060, 3000, 2955, 2930, 2832, 1504, 1495, 1257, 1028 cm"1; NMR (CDC13) i 2.10-2.50 (m, 2 H), 2.50-2.80 (m, 2 H), 3.83 (s, 3 H), 3.86 (s, 3 H), 5.44 (t, J = 7.03 Hz, 1 ), 6.51-6.92 (m, 3 ), 7.00-7.21 (m, 4 H); MS m/e 330 (6.5), 302 (10), 287 (13), 179 (100), 151 (43), 91 (77).…”

“…When the reaction was shown to be complete by TLC examination, but crystallization did not occur spontaneously, the solution was diluted with a 1:1 diethyl ether/benzene mixture and extracted with saturated aqueous sodium bicarbonate solution (2 X 50 mL), once with water (50 mL), and once with saturated aqueous sodium chloride solution (50 mL). The organic layer was dried (MgS04), and the solvent was removed in vacuo to leave a solid mass, which was recrystallized from methanol, yielding 76% of colorless needles: mp 138.5-139.5 °C; IR (CC14) v 2942, 2847,1612,1510,1462,1439,1250,1225,1199,1117,1070,1022,945 cm'1; NMR (CDC13) 8 1.81-2.10 (m, 2 ), 2.45-2.91 (m, 4 H), 3.85 (s, 6 ), 6.50 (s, 1 ), 6.90-7.20 (m, 4 ), 7.91 (s, 1 H); 13C NMR (CDClg) 8 20.77,29.44,42.35,56.22,71.91,112.04,113.77, 122.27,125.83,127.04,131.20,138.22,147.58,149.92; MS m/e 330 (100), 302 (62), 297 (46), 287 (33), 266 (24), 221 (14), 190 (20), 189 (45), 115 (17), 77 (13); UV (THF) X,^2 94 (log e = 3.82), 241 (log e 4.6), Xmax/ (log « = 4.4). Anal.…”

“…Method A provided colorless needles (0.17 g, 56%): mp 129.5-130.5 °C; IR (CC14) v 3060, 2941, 2846, 2840,1484,1441,1280,1250,1228,1112,1085,1014,956 cm"1; NMR (CDClg) 8 1.70-2.11 (m, 2 H), 2.45-2.63 (m, 2 H), 2.79 (t, J = 6.15 Hz, 2 H), 3.78 (s, 3 H), 3.82 (s, 3 H), 7.48 (dd, J = 14.7, J = 8.9 Hz, 2 H), 6.93-7.22 (m, 4 H); 13C NMR (CDClg) 20. 02, 23.58, 41.69, 55.85, 59.81, 71.25, 110.60, 122.04, 125.68, 126.03, 128.46,132.79,137.90,146.05,152.03; MS m/e 330 (100), 302 (10), (4), 297 (56), 287 (51), 266 (26), 221 (12), 190 (20), 189 (36), 115 (16), 77 (13); UV (THF) Xm" 302 (log « = 3.4), 241 (log « = 4.6), 222 (log í = 4.5). Anal.…”

“…2-(3,3',4,4',5,-Pentamethoxybenzhydryl)ethanal (13). To a suspension of sodium hydride (3.6 g, 150 mmol) (50% dispersion in oil, prewashed with pentane) in toluene (60 mL) at 0-10 °C was added dropwise triethyl phosphonoacetate (16.8 g, 75 mmol) in toluene (40 mL) over a period of 45 min.…”

“…The requisite substrate for testing this hypothesis was readily available in six steps from veratrole (Scheme II). Scheme II vided the known benzophenone 12 in 84% yield.11 Routine conversion to the aldehyde 13 followed in good overall yield and the labile ketene dithioacetal 11a was accessed in typically high yield by standard one-carbon homologation with reagent 5 as in previous cases. Exposure of 1 la to the standard cyclization conditions (trace of p-TsOH, 0 °C, several hours) provided the expected benzodithiole 14 as a single product in 86% yield.…”