Regioselective 15-bromination and functionalization of a stable synthetic bacteriochlorin.
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-Br15) 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 beta-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-Br15 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 approximately 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.
Fan
Dazhong
D
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
Taniguchi
Masahiko
M
Lindsey
Jonathan S
JS
D001966:Bromine / Q000737:chemistry*; D041961:Deuterium Exchange Measurement; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010165:Palladium / Q000737:chemistry; D011166:Porphyrins / Q000138:chemical synthesis* / Q000737:chemistry; D013053:Spectrophotometry; D013237:Stereoisomerism
D011166:Porphyrins; C452433:bacteriochlorin; D010165:Palladium; D001966:Bromine