反应详情

The triol from (b) above (0.5 g) in pyridine (0.5 ml) and acetic anhydride (8 ml) was heated at reflux for 1.5 hours. The solution was cooled, poured into ice-water and stirred to decompose the anhydride. Work up by extraction with ethyl acetate as usual gave a brown oil which was chromatographed on alumina (act. III, 25 g). Elution with hexane-benzene (7:3) gave a trace of non polar material. Benzene-hexane (1:1) yielded the title compound (0.58 g) as a very soluble colourless oil which resisted all attempts at crystallization. This material was homogeneous on t.l.c. on silica gel, alumina and silica gel-silver nitrate. νmax. (film) 1730 cm-1 (CDCl3) 5.50 (1 proton, narrow multiplet, H6), δ5.2-4.6 (2 protons, one broad and one narrow multiplet, H1 and H3 with H1 as a narrow multiplet at δ5.03), 2.00, 1.98, 1.91 (singlets, acetates), 1.40, 1.05, 0.67 (singlets, C26-27, C19, C18 methyls respectively.

1. temperatureat reflux for 1.5 hours
2. temperatureThe solution was cooled
3. extractionWork up by extraction with ethyl acetate
4. customas usual gave a brown oil which
5. customwas chromatographed on alumina (act. III, 25 g)
6. washElution with hexane-benzene (7:3)
7. customgave a trace of non polar material