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Synthesis of intermediates 3a and 3b: Compound 2 (1.89 g, 5.98 mmol) was dissolved in o-dichlorobenzene and triphenylphosphine (3.92 g, 14.85 mmol) was added to a double neck flask. Subsequently, the reaction mixture was heated to reflux and stirred continuously for 24 hours. During the reaction, the color of the solution changed from yellow to brown. Upon completion of the reaction, the mixture was cooled to room temperature and concentrated by distillation under reduced pressure. Eventually, the products were purified using silica gel column chromatography to afford intermediates 3a and 3b in 45% yield, respectively.

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