[O:1]1[C:10]2[C:5](=[CH:6][CH:7]=[CH:8][CH:9]=2)[C:4](=O)[CH2:3][CH2:2]1.O1C2C(=CC=CC=2)CCC1.[Li]CCCC.[C:27](=[O:29])=[O:28]>C(O)(=O)C.[Zn]>[O:1]1[C:10]2[C:5](=[CH:6][CH:7]=[CH:8][C:9]=2[C:27]([OH:29])=[O:28])[CH2:4][CH2:3][CH2:2]1
Commercially available 3-hydroxy-benzoic acid methyl ester (47) is alkylated with propargyl bromide in the presence of K2CO3 to give phenylether (48) which is cyclized to the chromen derivative (49) by heating to reflux in N,N-diethylaniline. The carboxylic ester is saponified by treatment of (49) with NaOH in MeOH/water and the obtained chromen derivative (50) is hydrogenated in presence of a palladium catalyst to give the desired acid (51). The corresponding chroman-8-carboxylic acid derivatives are synthesized by reduction of commercially available 4-chromanone (52) with zinc in acetic acid and subsequent ortho-metalation of the intermediate chroman derivative (53) with n-BuLi and trapping with carbon dioxide to give the desired acid (54).
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