One-Pot Bromination and Dehydrobromination

Significance

The silica gel entrapped bromination reagent, pyridinium hydrobromide perbromide 1 (PHPB@s.g.), was prepared by treatment of 2-[2-(trimethoxysilyl)ethyl]pyridine with concentrated hydrobromic acid and bromine followed by hydrolysis and co-condensation with tetra­methoxysilane (TMOS). The entrapped reagent 1 was used for the bromination of alkenes, ketones, and arenes (eq. 1), and was recycled four times with recharge of bromine. One-pot bromination and dehydrobromination processes were achieved by use of 1 and a silica gel entrapped guanidine base 2 (TBD@s.g.) which was prepared from 1,5,7-triaza­bicyclo[4.4.0]dec-5-ene (TBD) via similar silica sol-gel entrapping to give vinyl bromides or ace­tylenes (eq. 2).