1-Bromo-2-iodo-2-butene1

[147644-04-0]  · C4H6BrI  · 1-Bromo-2-iodo-2-butene  · (MW 260.90)

(organopalladium Heck annulation)

Handling, Storage, and Precautions: as a low molecular weight allylic halide, this reagent can be expected to be lachrymatory; irritating to, and absorbed through, the skin and mucous membranes; especially hazardous via inhalation; suspect carcinogen. As an iodoalkene, it can be expected to be photochemically and/or thermally labile and susceptible to oxidation in air. Use in a fume hood.

Annulation.

In a new approach to Strychnos alkaloids, Rawal deployed 1-bromo-2-iodo-2-butene for construction of ring E via N-alkylation followed by Pd-catalyzed cyclization (intramolecular Heck reaction). Thus the reagent of (Z) configuration led to racemic dehydrotubifoline with correct exocyclic double bond stereochemistry (eq 1).1 Prior model experiments demonstrated the stereospecific nature of the cyclization (eqs 2 and 3).2 The requisite diastereomeric iodoalkenes were obtained by regio- and stereoselective addition of Tri-n-butylstannane to 2-butyn-1-ol, followed by iododestannylation (eqs 4 and 5).2


1. Rawal, V. H.; Michoud, C.; Monestel, R. F. JACS 1993, 115, 3030.
2. Rawal, V. H.; Michoud, C. TL 1991, 32, 1695.

Raymond E. Conrow

Alcon Laboratories, Fort Worth, TX, USA



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