General procedure for the synthesis of tetrahydropyran-3-carbaldehyde from 5,6-dihydro-2H-pyran-3-carbaldehyde: 10% Pd/C catalyst (600 mg) was slowly added to a solution of 5,6-dihydro-2H-pyran-3-carbaldehyde (6 g, 53.5 mmol) in methanol (10 mL). The reaction mixture was stirred under hydrogen (40 psi) atmosphere. Upon completion of the reaction, the reaction mixture was filtered through diatomaceous earth, the precipitate was washed with methanol and the filtrate was concentrated under vacuum. The residue was purified by fractional distillation at 125°C/20 mmHg to afford tetrahydropyran-3-carbaldehyde (5.5 g, 91.6% yield). Mass spectral (MS) data (m/z): [M + H]+, 115.1.
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