Procedure A. Ethyl (E)-4-hydroxy-2-pentenoate (1)An oven-dried, 1000-mL, two-necked, round-bottomed flask equipped with a rubber septum, an argon inlet, and a magnetic stirbar was purged with argon and charged with Et 2 O (500 mL) (Note 1) and ethyl (E)-4-oxo-2-butenoate (24.1 mL, 25.6 g, 200 mmol, 1.0 equiv) (Note 2).The solution was cooled to -78 °C in a dry ice/acetone bath, and then MeMgBr (3.0 M in Et 2 O; 70.0 mL, 210 mmol, 1.05 equiv) (Note 3) was added dropwise via syringe pump (2.0 mL/min) over 35 min (The slow addition can also be conducted via a 100-mL pressure-equalizing addition funnel fitted with a septum).After the addition was complete, the reaction mixture was stirred for an additional 2 h at -78 °C.During the course of the reaction, the precipitation of white solids led to a heterogeneous reaction mixture.The progress of the reaction can be followed by TLC analysis on silica gel (20% Et 2 O/hexanes as the eluent; visualization with a UV lamp or with a KMnO 4 stain; the aldehyde starting
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Lou et al. (2010) studied this question.