Novel stereochemical rearrangement process for an isomer of trimethylsilicon acetylacetonate, a silyl enol ether

Abstract

after stirring 5 min the mixture was washed with 1 N HC1 and NaHCOa solution, dried, and evaporated.The residue was dissolved in benzene, filtered to remove some dicyclohexylurea, and chromatographed on 150 g of silica gel. Elution with 20-100% ethyl acetate in Skellysolve B gave major peaks corresponding to epimeric glycols of structure 4 (R = CH2CC13). The less polar, 700 mg, showed one spot on tic-silica gel, 50% ethyl acetate-cyclohexane; the more polar, 800 mg, showed two very close spots on the same tic system. The R¡ values of these trichloroethyl esters were similar but slightly greater than those of the corresponding methyl esters, above.To 667 mg of the less polar glycol 4 (R = CH2CC13) above was added 16.5 ml of pyridine and then, at 0°, 1.67 ml of methanesulfonyl chloride. The mixture was stirred at 0°for 10 min, and 1.75 hr longer with the ice bath removed. It was then again cooled to 0°, 15 ml of water was added, and the mixture was extracted with ethyl acetate. This was washed several times with cold dilute hydrochloric acid and aqueous sodium bicarbonate, dried, and evaporated. The crude bismesylate was stirred in 53 ml of acetone and 26 ml of water under nitrogen at 25°o vernight. The solution was concentrated in vacuo and extracted with ethyl acetate, which was washed, dried, and evaporated. The residue was chromatographed on 75 g of silica gel and eluted with increasing amounts of ethyl acetate in Skellysolve B. After two main peaks of material, 276 and 103 mg, of unrearranged glycol monomesylates was eluted 34 mg of ¿/-8-isoprostaglandin Ei trichloroethyl ester showing two olefinic protons between 5.0 and 6.0 ( 33 at 5.28,7=15 and 9.5 cps, and Hu at 5.7, 7=15 and 7 cps), two protons of the trichloroethyl group as a singlet, 4.8, and two carbinolic protons as multiplets between 3.9 and 4.5. This was followed by 12 mg (5) L. H. Piette and W. A. Anderson, J. Chem. Phys., 30, 899 (1959), eq 23.

Chemistry of enol silyl ethers. 5. A novel cycloaromatization reaction. Regiocontrolled synthesis of substituted methyl salicylates

“…in C6D6 similar to that reported in PhCl. 19 4-TrimethyIsiloxy-4-phenylbut-3-en-2-one (5). Prepared as for 2 above (0.05-mol scale), 5 (94%) was a colorless oil: bp 105-107 °C (0.15 mm) [lit.20 110-111 °C (0.2 mm)]; NMR (CDC13) a 3:1 mixture of isomers, 0.22 (minor) and 0.34 (major) (each s, 9 H, Me3Si), 2.20 (minor) and 2.38 (major) (each s, 3 H, Me), 5.91 (minor) and 6.21 (major) (each s, 1 H, -CH=), 7.2-7.9 (m, 5 H, Ph); IR (film) 1658, 1598, 1586, 1574 cm"1.…”

Thermal rearrangements of reactive intermediates in organosilicon chemistry

“…This is considerably lower than that of the 1,3-silicon migration in allylsilanes (Ea = 48 kcal/mol) and the 1,5-hydrogen migra tion in the silylcyclopentadienes (Ea -26 kcal/mol). In fact, only at -10°C could distinct vinylic protons be observed by NMR, In 1969,it was shown by Howe and Pinnavaia that trialkylsilyl acetylacetonates exist as an equilibrium mixture of ci s and trans isomers (20). For example, the ratio of IJ to 12 is 0.66 at room tenperat'jrs.…”

Thermal rearrangements of reactive intermediates in organosilicon chemistry

“…In 1969,it was shown by Howe and Pinnavaia that trialkylsilyl acetylacetonates exist as an equilibrium mixture of ci s and trans isomers (20). For example, the ratio of IJ to 12 is 0.66 at room tenperat'jrs.…”