Synthesis of 6-(1-Hydroxyethyl)-2,2-dimethyl-2H--benzopyrans: Eupatoriachromene-C and Desmethoxyencecalinol
6-Acetyl-5,8-dimethoxy-2,2-dimethyl-2H--benzopyran (2) on reduction with potassium borohydride gives eupatoriochromene-C (1).Condensation of 4-Hydroxyacetophenone with isoprene in the presence of orthophosphoric acid gives the chroman (5) which on dehydrogenation with NBS furnishes desmethoxyencecalin (4). 4 on reduction with potassium borohydride affords desmethoxyencecalinol (3).Alternatively, 4-hydroxybenzaldehyde on condensation with isoprene gives the monochroman (6) which is also obtained by a similar condensation of 4-methylphenol with isoprene followed by reaction with DDQ.Dehydrogenation of 6 with NBS affords 6-formyl-2,2-dimethyl-2H--benzopyran (8) and 6-phenacyl bromide derivative (9). 8 on reaction with methylmagnesium iodide furnishes 3.
Ahluwalia, V. K.,Mukherjee, Irani,Mukherjee, Keya
p. 1124 - 1125
(2007/10/02)
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