[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]1The synthesis of chroman-5-carboxylic acid derivatives started with the alkylation of 3-hydroxy-benzoic acid methyl ester (49; commercially available) with propargyl bromide in the presence of K2CO3 to give phenylether (50) which was cyclised to the chromen derivative (51) by heating to reflux in N,N-diethylaniline. The carboxylic ester was saponified by treatment of (51) with NaOH in MeOH and water and the obtained chromen derivative (52) was hydrogenated to give the desired acid (53). The corresponding chroman-8-carboxylic acid derivatives were synthesized by reduction of 4-chromanone (54; commercially available) with zinc in acetic acid and subsequent ortho-metalation of the intermediate chroman derivative (55) with n-BuLi and trapping with carbon dioxide to give the desired acid (56).
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