Base Promoted Rearrangement of Carbonate Esters Derived from Aldehyde Cyanohydrins: Application to the Synthesis of α-Keto Esters

References

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• Purchased from Fluka
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• Mixed carbonate esters (3) were prepared under a nitrogen atmosphere by slow, dropwise addition of excess ethyl chloroformate (2.00 mL, 20.9 mmoles) to a solution of 5.0 mmoles of cyanohydrin 2 in 0.50 mL (6.2 mmoles) of anhydrous pyridine at 0°C, and subsequent stirring at 20°C for 15 hours. Prior to isolation of the product (3) via ether extraction, the mixture was cooled to 0°C and excess acid chloride was destroyed by slow, dropwise addition of a mixture of ether (10 mL) and water (1 mL)
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• IR: vmax (film) 3460 (OH), 1762 (C[dbnd]O, 4a), 1740 (ester carbonyl, 5a), 1695 (C[dbnd]O, 5a) cm−1
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• bp 83–92°C (bath temperature, 0.20 mm); 1H NMR δ (CDC13) 5.27 (t, J = 7 Hz, CHCN), 4.30 (quartet, J = 7.5 Hz, OCH2CH3), 1.38 (t, J = 7.5 Hz, OCH2CH3), 1.02 [d, J = 6.5 Hz, (CH3)2CH]. Satisfactory (± 0.10%) elemental analysis (C,H,N) was obtained for this novel compound
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• The physical and spectral properties of keto ester 5b were identical with those previously published7 with one notable exception. The proton NMR spectrum exhibited a doublet at δ 2.72 (CH2C[dbnd]O), not at δ 3.72 as reported7 (undoubtedly as a typographical error) by J. Singh and coworkers
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