A Convenient Route to 2-Bromo-3-chloronorbornadiene and 2,3-Dibromonorbornadiene
Received: 05 March 2015
Accepted after revision: 15 April 2015
27 May 2015 (eFirst)
This paper is dedicated to Prof. K. P. C. Vollhardt on occasion of his 69th birthday. Thank you for inspirational leadership and enlightening supervision.
Substituted norbornadienes are useful in a wide range of applications, including molecular solar-thermal (MOST) energy storage systems. An important precursor for 2,3-substituted norbornadienes is 2-bromo-3-chloronorbornadiene, where the two halogen atoms can be substituted selectively through two consecutive Suzuki cross-coupling reactions. Previous routes to 2-bromo-3-chloronorbornadiene have used 1,2-dibromoethane as a brominating agent, a substance known to be carcinogenic and the use of which is restricted in certain countries. Herein is reported a one-pot route to 2-bromo-3-chloronorbornadiene in 50% yield using p-toluenesulfonyl bromide as a bromine source. In addition, the procedure has been adapted to allow synthesis of 2,3-dibromonorbornadiene in 37% yield.