Silica sol‐gel encaged pyridinium hydrobromide perbromide can be used for clean, odorless bromination of a variety of substrates, including alkenes, ketones, and arenes. The used heterogenized bromination reagent can be recharged with bromine and recycled. In the presence of sol‐gel entrapped 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene, dibromides are dehydrobrominated to give vinyl monobromides and/or alkynes. Encapsulation of the pyridinium derivative and the guanidine base within separate sol‐gel matrices enables the use of both opposing reagents in one‐pot reactions without their mutual destroying each other. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Halogenation O 0235Sol-Gel Entrapped Pyridinium Hydrobromide Perbromide as a Recyclable Bromination Agent: Its Application to a One-Pot Bromination and Dehydrobromination Process. -The reagent can be used for the clean, odorless bromination of a variety of substrates including alkenes (I), ketones (III) and arenes (V). The heterogenized reagent can be recharged with bromine and recycled. One-pot bromination/dehydrobromination reactions are carried out in the presence of sol-gel supported 1,5,7-triazacyclo[4.4.0]dec-5-ene; the use of both reagents (pyridinium derivative and guanidine base) in one-pot is enabled by encapsulation within separate sol-gel matrices.-(LEVIN, Y.; HAMZA, K.; ABU-REZIQ, R.; BLUM*, J.; Eur.