Synthesis and Chiroptical Properties of L‐Serine‐Based Poly(phenylacetylenes)

L‐Serine‐based hydroxy group‐containing phenylacetylene, N‐(α‐tert‐butoxycarbonyl)‐L‐serine 4‐ethynylphenylamide (1), and the hydroxy group‐protected counterpart, N‐(α‐tert‐butoxycarbonyl)‐O‐trimethylsilyl‐L‐serine 4‐ethynylphenylamide (2) were polymerized with (nbd)Rh⁺[η⁶‐C₆H₅B⁻(C₆H₅)₃] as a catalyst to obtain the corresponding polymers [poly(1) and poly(2)] with moderate molecular weights in good yields. The polarimetric and CD spectroscopic data indicated that poly(1) existed in a helical conformation in DMF, MeOH, and THF; and that poly(2) also took a one‐handed helical structure in CHCl₃ and toluene in addition to these solvents. The helical tightness of poly(2) depended on the polarity of the solvents. Upon heating, poly(1) and poly(2) slightly decreased the CD intensity in DMF, MeOH and THF, while poly(2) increased it in toluene. The helical conformation of poly(1) and poly(2) was stable by adding cyclohexane to THF.

Keywords:

• L‐serine
• poly(phenylacetylene)
• helix

5 Acknowledgement

This research was partly supported by a Grant‐in‐Aid for Science Research in a Priority Area “Super‐Hierarchical Structures (No. 446)” from the Ministry of Education, Culture, Sports, Science and Technology, Japan.