中文名称 | 英文名称 | CAS号 | 化学式 | 分子量 |
---|---|---|---|---|
—— | [(6R,9R,10S)-9-[(2S)-6-(2-ethyl-1,3-dithiolan-2-yl)-5-hydroxy-4-methyl-3-oxoheptan-2-yl]-6,10-dimethyl-1,4,8-trioxaspiro[4.5]decan-7-yl] 2,2-dimethylpropanoate | 1228184-05-1 | C27H46O7S2 | 546.79 |
—— | (6R,7RS,9R,10S)-6,10-dimethyl-9-((S)-3-oxopentan-2-yl)-1,4,8-trioxaspiro[4.5]decan-7-yl pivalate | 1415754-67-4 | C19H32O6 | 356.459 |
A versatile three-step procedure to annulate a γ-pyrone onto a methylene ketone was developed involving (i) aldol reaction with a dithiolane-protected β-ketoaldehyde, (ii) oxidation of the aldol adduct to a β-diketone, and (iii) treatment of the resulting dithiolane-protected 1,3,5-trione with 2-iodoxybenzoic acid (IBX) and trifluoromethanesulfonic acid (triflic acid; TfOH) in acetonitrile at ambient temperature to give the corresponding γ-pyrone. Cyclization proceeded with IBX alone, but significantly improved yields were obtained with added acid, particularly triflic acid. A dithiolane was more effective than a dithiane or acyclic dithioacetal protecting group. The method was amenable to the preparation of a variety of substituted γ-pyrones simply by altering the initial aldol reactants. Overall yields of 50%–60% were obtained in six examples. The method was applied to prepare a key fragment for the total synthesis of baconipyrones A and C and siphonarin B.