Diastereodifferentiating Photocyclodimerization of 2‑Anthracenecarboxylates Tethered to a Cyclic Tetrasaccharide Scaffold: Critical Control of Photoreactivity and Stereoselectivity

• Published in: Journal of organic chemistry Vol. 78; no. 21; pp. 10996 - 11006
• Main Authors: Fukuhara, Gaku, Nakamura, Tomohiro, Kawanami, Yuko, Yang, Cheng, Mori, Tadashi, Hiramatsu, Hiroyuki, Dan-oh, Yasufumi, Nishimoto, Tomoyuki, Tsujimoto, Kazuo, Inoue, Yoshihisa
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 01.11.2013; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; CIRCULAR-DICHROISM; 2+2 PHOTOCYCLOADDITION; ASYMMETRIC INDUCTION; DIASTEREOSELECTIVITY; CHIRAL INDUCTION; ANTHRACENE; PATERNO-BUCHI REACTION; PHOTOCHEMICAL-REACTIONS; PHOTOCHIROGENESIS; CHARGE-TRANSFER EXCITATION
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo401977f

From a complex mixture of mono- and di-2-anthracenecarboxylic acid (AC) esters of cyclic nigerosylnigerose (CNN), two monoesters (2 B and 6 A ) and four diesters in which AC was introduced on the transannular B/D (2 B 2 D ), adjacent A/B and A/D (6 A 2 B and 6 A 2 D ), and same B/B (2 B 3 B ) nigerose rings were isolated. Possessing two ACs at distant positions, 2 B 2 D and 6 A 2 D showed negative Cotton effects for the 1Bb band, the intensities of which were stronger than that of 6 A . 2 B 2 D and 6 A 2 D slowly photocyclodimerized to give HH dimers 3* and 4 with 57% and 81% HH selectivity, respectively, which were appreciably higher than that for 6 A (34%), while the enantiomeric excesses (ee’s) of anti-HH dimer 3* were 2% and −18%, respectively. In contrast, 6 A 2 B and 2 B 3 B carrying two ACs on adjacent A and B rings or at vicinal positions on the B ring, respectively, exhibited strong positive CD couplets, the amplitudes of which amounted to 97 and 409 M–1 cm–1, respectively. Upon irradiation, 6 A 2 B afforded 3* with −62% ee and 4 in 96% combined yield, whereas 2 B 3 B gave almost exclusively 3* with −99% ee in 96% yield, likely as a result of the introduction of two ACs at the vicinal positions of the rigid CNN scaffold.