(S)-3,5-di-(tert-butyldimethylsilyloxy)-pentan-2-one → (S,4E)-1,3-Di-(tert-butyldimethylsilyloxy)-4-methyl-5-(2-methylthiazol-4-yl)-pent-4-ene

Participants

Reaction Conditions

Reaction Steps

(see D. Schinzer et al., Chem. Eur. J. 2, 1477-1482 (1996)) n-Butyl lithium (23,5 ml [58.7 mmol, 1.2 equiv] of a 2.5 M solution in hexanes) is added dropwise to a stirred solution of diethyl-(2-methylthiazol-4-yl)-methanephosphonate 10 (14,64 g, 58.7 mmol, 1.2 equiv) in THF (150 ml) cooled to −78° C. After stirring at −78° C. for 1 h, a solution of (S)-3,5-di-(tertbutyidimethylsilyloxy)-pentan-2-one 14 (16.96 g, 48,9 mmol, 1.0 equiv) in 100 ml of THF is added dropwise at −78° C. The mixture is warmed to r.t. within 12 h. The reaction is quenched with saturated aqueous ammonium chloride solution (100 ml). The organic layer is seperated and the aqueous layer is extracted with diethyl ether (3×100 ml). The combined organic extracts are dried over magnesium sulfate and concentrated in vacuo. Purification of the residue by flash column chromatography (gradient elution with pentane/dichloromethane 4:1→dichloromethane→diethyl ether→diethyl ether/methanol 10:1) affords (S,4E)-1,3di-(tert-butyldimethylsilyloxy)-4-methyl-5-(2-methylthiazol-4-yl)-pent-4-ene 15 (17,07 g, 38.6 mmol, 79%) as a colourless oil and some starting material (10 and 14). Alternatively, the crude product obtained after extraction can be directly used in the next step.

Provenance & Evidence