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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.

concept of boron masking.jpg

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.

masked modules80.jpg

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.

synthesis of oligoarenes80.jpg
 

References

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

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