Process for the preparation of pgd2 antagonist

A process for the preparation of a compound of formula 8 or a salt thereof,

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• which comprises the steps of:
• (1) treating the compound (1R)-(+)-nopinone with a strong base to generate the corresponding enolate;
• (2) reacting the enolate with X—CH2—C≡C—(CH2)3CO2R where X is a leaving group and R is C1-5alkyl to provide the compound 3a
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• (3) reacting compound 3a with hydroxylamine to provide compound 4a
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• (4) treating compound 4a with titanium (III) chloride and a borane reagent to provide compound 5a
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• (5) treating compound 5a with hydrogen in the presence of a hydrogenation catalyst to provide compound 6a
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• (6) reacting the compound 6a with 5-hydroxy-4-benzo[b]thiophenecarboxylic acid in the presence of coupling agent, or an acylating equivalent thereof, followed by base-catalyzed hydrolysis to provide compound 8.