Methyl 2-Diazo-3-butenoate

Abstract

[126554-35-6] C5H6N2O2 (MW 126) InChI = 1S/C5H6N2O2/c1-3-4(7-6)5(8)9-2/h3H,1H2,2H3 InChIKey = RCHAWIWORXGKLB-UHFFFAOYSA-N (precursor to highly chemoselective metal carbenoids) Physical Data: IR (neat) 2082, 1695, 1610 cm−1; 1H NMR (CDCl3) δ6.15 (dd, J = 17.4, 11.0 Hz, 1H), 5.01 (d, J = 11.0 Hz, 1H), 4.94 (d, J = 17.4 Hz, 1H), 3.79 (s, 3H). Solubility: soluble in most organic solvents including hydrocarbons. Form Supplied in: not commercially available. Preparative Methods:1 a solution of n-butyllithium (41.2 mL, 65.6 mmol, 1.6 M in hexanes) was added to a solution of diisopropylamine (10.12 mL, 72.2 mmol) in diethyl ether under argon at −78 °C. The solution was allowed to warm to ambient temperature for 15 min and then cooled again to −78 °C. HMPA (16.8 mL, 65.6 mmol) was then added and the mixture was stirred for 30 min. A solution of methyl but-3-en-1-oate (3.28 g, 32.8 mmol) in diethyl ether (5 mL) was then added and the mixture stirred for 30 min. At this time, a solution of p-toluenesulfonyl azide (12.94 g, 75.6 mmol) in diethyl ether (10 mL) was added and the solution was warmed to ambient temperature over 12 h. Water was then added and the mixture was extracted with pentane. The organic layer was washed with water, brine, and then dried over MgSO4. The solvent was removed under reduced pressure at 15–20 °C and the residue was rapidly purified by flash chromatography (silica gel, diethyl ether/pentane, 1/9) to give the title compound as an orange oil (3.0 g, 73% yield). Note: A convenient, one-pot protocol has been recently developed for the synthesis of a variety of aryl- and heteroaryl-substituted vinyldiazoacetates from the respective aryl aldehydes.2, 3 Other methods for the synthesis of substituted vinyldiazoacetates are the dehydration of β-hydroxy-α-diazoacetates,4, 5 the silylation of β-keto-α-diazoacetates,6, 7 and the cross coupling of diazoacetates with vinyl halides.8 Purification: The title compound can be readily purified by flash chromatography on silica gel with a diethyl ether/pentane solvent system to give an orange oil. Handling, Storage, and Precautions: The title compound is volatile under reduced pressure. As such, care should be taken to use the minimum amount of vacuum required for concentration of the diazoacetate-containing solution after purification. The diazo compound will, upon standing, slowly undergo an electrocyclization reaction to form a pyrazole. This reaction can be slowed considerably by storing the diazo compound as a solution in pentane at 0 °C or below. Under such conditions the diazo compound is stable to electrocyclization for several days. As with all diazo compounds, however, caution should be exercised in handling this compound and excessive heating should be avoided. As a precaution, it is recommended that all procedures using this compound should be conducted behind a blast shield.