Regioselective 15-Bromination and Functionalization of a Stable Synthetic Bacteriochlorin

Publisher Website
Google Scholar
Abstract
5-Methoxy-8,8,18,18-tetramethyl-2,12-di-p-tolylbacteriochlorin (MeO - BC) undergoes regioselective electrophilic bromination with NBS to give the 15-bromo analogue (MeO - BC - Br 15) in 85% yield. By contrast, the bacteriochlorin lacking the 5-methoxy group (8,8,18,18-tetramethyl-2,12-di-p-tolylbacteriochlorin, H - BC) gives a mixture of two monobromo- and two dibromobacteriochlorins. Deuterium exchange of both bacteriochlorins (H - BC and MeO - BC) in acidic media (TFA-d) occurs preferentially at the β-pyrrole positions (3, 13) > unhindered meso-positions (5, 15 for H - BC; 15 for MeO - BC) > hindered meso-positions (10, 20). The 15-bromo-5-methoxybacteriochlorin MeO - BC - Br 15 was subjected to three types of Pd-mediated coupling reactions (Suzuki, Sonogashira, Hartwig−Buchwald) to give six bacteriochlorins bearing functional groups at the 15-position (49% to 85% yield). The groups include 4-(tert-butoxycarbonylmethoxy)phenyl, 4-pyridyl, 3,5-diformylphenyl, phenylethynyl, TIPS-ethynyl, and N-benzamido. The presence of the 15-ethynyl moiety shifts the position of the long-wavelength Qy band from 732 nm to ∼753 nm. The ability to introduce a range of groups at a specific site enables synthetic bacteriochlorins to be tailored for a variety of applications.

This publication has 44 references indexed in Scilit: