*Boron-Masking Strategy for the Module-Based Iterative Cross-Coupling
Our particular attention has focused on the protection of the boronyl groups (B(OH)SUB{2};) in the Suzuki–Miyaura coupling, because the protection would lead to the iterative coupling system in which protected monomers are repeatedly coupled. In the iterative cross-coupling system, the temporary mask of the B(OH)SUB{2}; group (indicated by M) plays a key role.
#ref(Graphics for Reserch/concept of boron masking.jpg,center)
We established 1,8-diaminonaphthalene as a protective group of the boronyl groups [Ref. 1]. The protective group could be easily installed in high yields by the condensation of organoboronic acids with 1,8-diaminonaphthalene and could be deprotected in high yields by treatment with aqueous acids.
#ref(Graphics for Reserch/masked modules80.jpg,center)
The protected haloarylboronic acids were coupled with organoboronic acids in excellent yields under the ordinary Suzuki–Miyaura coupling conditions. Starting with the coupling of masked haloarylboronic acid ''B’'' with arylboronic acids ''A'', deprotection and coupling were repeated four times more, resulting in the formation of quinquearyl ''A''-''B''-''B''-''C''-''C’'' selectively.
#ref(Graphics for Reserch/synthesis of oligoarenes80.jpg,center)
#br
**References
-Ref. 1
--Boron-Masking Strategy for the Selective Synthesis of Oligoarenes via Iterative Suzuki-Miyaura Coupling H. Noguchi, K. Hojo, M. Suginome, '''J. Am. Chem. Soc.''' ''2007'', 129, 758-759, [[10.1021/ja067975p>http://dx.doi.org/10.1021/ja067975p]]
--Differentially Protected Benzenediboronic Acids: Divalent Cross-Coupling Modules for the Efficient Synthesis of Boron-Substituted Oligoarenes H. Noguchi, T. Shioda, C.-M. Chou, M. Suginome, '''Org. Lett.''' ''2008'', 10, 377-380, [[10.1021/ol702420x>http://dx.doi.org/10.1021/ol702420x]]
**Acknowledgement
This work was supported by The Ministry of Education, Culture, Sports, Science and Technology (MEXT). Grant-in-Aid for Scientific Research (A), KAKENHI (19205007). [[Link:http://www.jsps.go.jp/english/e-grants/grants.html]]
