Sodium borohydride → 5-Hydroxy-6-(1-hydroxypropyl)-2,2-dimethyl-10-propyl-pyrano[2,3-f]chromen-8-one

Beteiligte Stoffe

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Reaktionsschritte

A solution of 5-hydroxy-2,2-dimethyl-6-propionyl-10-propyl-2H-pyrano[2,3-f]chromen-8-one (30) (10.0 g, 29.2 mmol, 1.0 eq) in a mixture of ethanol (500 mL) and THF (200 mL) was cooled to 0° C. and sodium borohydride (1.7 g, 45.0 mmol, 1.54 eq) was add portionwise within 1 h. The reaction mixture was allowed to warm up room temperature and stirred for 3.5 h. The reaction was quenched with saturated aqueous ammonium chloride (20 mL). The solvents were removed under vacuum and the residue was partitioned between ice-cold 1N hydrochloric acid (200 mL) and ethyl acetate (500 mL). The organic layer was separated and washed successively with saturated sodium bicarbonate (200 mL) and brine (200 mL). The organic solution was dried over anhydrous sodium sulfate and concentrated under vacuum. The product was purified on a silica column eluted with 20-50% ethyl acetate in hexanes, affording 7.1 g of 11a (71% yield). 1H NMR (CDCl3): 1.01 (q, J=7.5 Hz, 6H), 1.46 (s, 3H), 1.50 (s, 3H), 1.61 (m, 2H), 1.88 (m, 2H), 2.78 (m, 1H), 2.89 (m, 1H), 4.96 (d, J=3.5 Hz, 1H), 5.54 (d, J=10.0 Hz, m, 2H), 5.78 (s, 1H), 6.69 (d, J=10.0 Hz, 1H), 10.18 (s, 1H); 13C NMR (CDCl3): 9.57, 14.04, 23.10, 27.47, 28.08, 29.78, 38.59, 70.73, 77.58, 102.85, 107.15, 107.62, 109.12, 116.54, 126.76, 150.89, 151.28, 156.08, 159.70, 162.01; IR: 1683 cm−1; MS (ACPI+): 345 (M+1); Anal. Calcd. for C20H24O5: C 69.75, H 7.02; Found: C 69.90, H 7.05.

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