· t-Butyl (E)-4-Iodo-2-methyl-2-butenoate
· (MW 282.12)
(regioselective annulations;1 methyl vinyl ketone equivalent2)
Alternate Name: t-butyl g-iodotiglate.
Physical Data: bp 80 °C/0.005 mmHg.1
Preparative Method: treatment of Chloroacetaldehyde with the phosphorane shown in eq 1 followed by halogen exchange with Sodium Iodide/acetone affords the title reagent in 76% overall yield.1,2
The title reagent is a Methyl Vinyl Ketone equivalent and has been employed in Robinson annulation reactions. A cyclohexanone derivative (lithium enolate or enamine) is alkylated with the iodobutenoate. Subsequent hydrolysis of the alkylated intermediate with p-Toluenesulfonic Acid affords the unsaturated carboxylic acid in 80-90% combined yield (eq 2).1,2 An oxidative decarboxylation procedure (eq 3) via a Curtius rearrangement of the derived acyl azide affords an ene carbamate. Basic hydrolysis of the carbamate followed by an in situ base-catalyzed aldol condensation completes the cyclohexenone annulation in 75-90% overall yield from the carboxylic acid intermediate.1-3
- 1. (a) Gawley, R. E. S 1976, 777; (b) Hill, K. H. Ph.D. Thesis, University of Texas, Austin, TX, 1972.
- 2. (a) Stotter, P. L.; Hill, K. A. TL 1975, 16, 1679. (b) Stotter, P. L.; Hill, K. A. JACS 1974, 96, 6524.
- 3. Weinstock, J. JOC 1961, 26, 3511.
Jeffrey S. DePue
University of Illinois, Urbana, IL, USA
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