· (MW 73.11)
(O-allyloximes, pyridine synthesis)
Alternate Name: O-2-propenylhydroxylamine.
Physical Data: bp 80 °C, IR 3350 cm-1. The reagent is typically prepared as the hydrochloride salt which is a white solid that may be recrystallized from EtOH and ether.
Preparative Methods: Allyl Bromide (39 mL, 0.46 mol) is added dropwise with stirring to a suspension of anhydrous K2CO3 (43 g) and commercially available N-hydroxyphthalimide (50 g, 0.31 mol) in DMSO (500 mL) at 25 °C. After addition, the mixture is stirred at room temp for 24 h and then poured into cold water (3 L). The precipitate is collected, washed with water, and dried. Recrystallization from EtOH gives N-allyloxyphthalimide (87%), mp 56-57 °C. A mixture of N-allyloxyphthalimide (10 g, 0.05 mol), hydrazine hydrate (5 mL, 0.1 mol), and EtOH (100 mL) is refluxed for 2 h and then cooled and poured into 3% aqueous Na2CO3 (500 mL). The solution is extracted with ether. The ether
extract is washed with water and then 5 mL of conc HCl are added. Evaporation gives a solid which is recrystallized from EtOH and ether to afford O-allylhydroxylamine hydrochloride as a white solid (eq 1). The free amine can be liberated by distillation from KOH (bp 80 °C)1 or by treatment with ammonia in situ.2 It may be conveniently stored as the N-allyloxphthalimide intermediate which is converted to O-allylhydroxylamine hydrochloride as needed.
Handling, Storage, and Precautions: use in a fume hood.
Synthesis of Pyridines.
The reagent reacts with ketones to provide O-allyloximes in generally good yields. These materials may, in turn, be pyrolyzed by heating in a sealed tube at about 180 °C to undergo an electrocyclization which has been proposed to proceed through a nitrile oxide intermediate.1,2 The final step involves oxidation of a dihydropyridine and therefore it is important not to exclude air from the pyrolysis. The intermediate in eq 2 can be derived by allylation of the corresponding oxime; however, this process is generally inferior to the O-allylhydroxylamine approach.
Twofold application of this method to provide bipyridines is unsuccessful. The bridged bipyridine which would be derived from 1,2-cyclooctanedione is better prepared by a stepwise approach wherein the product of eq 2 can be converted to its a-keto derivative and then the second pyridine ring incorporated as before (eq 3).3,4
- 1. Koyama, J.; Sugita, T.; Suzuta, Y.; Irie, H. CPB 1983, 31, 2601.
- 2. Kusumi, T.; Yoneda, K.; Kakisawa, H. S 1979, 221.
- 3. Wang, X. C.; Cui, Y. X.; Mak, T. C. W.; Wong, H. N. C. CC 1990, 167.
- 4. Thummel, R. P.; Lefoulon, F.; Mahadevan, R. JOC 1985, 50, 3824.
Randolph P. Thummel
University of Houston, TX, USA
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