Stereospecific Synthesis of cis-2,5-Disubstituted Pyrrolidines via N,O-Acetals Formed by Hydroamination Cyclization-Hydroalkoxylation of Homopropargylic Sulfonamides in HFIP.

We reported a novel two-step stereoselective synthesis of functionalized pyrrolidines from homopropargylic sulfonamides and nucleophiles via an isolable N,O-acetal intermediates. This reaction features mild conditions and good scope of substrates. In addition, the use of hexafluoroisopropanol, acting as a solvent, an additive, a weak nucleophile, and a good leaving group, is pivotal to the success of the method. Moreover, reactions of chiral homopropargylic sulfonamides afford only 2,5-cis-disubstituted pyrrolidines with high diastereoselectivity (up to >99:1 dr) and enantioselectivity (up to >99% ee). The overall reaction constitutes a formal 1,1-bifunctionalization of terminal alkynes, which has hitherto been reported only rarely. Additionally, this method provides efficient access to pharmaceutical intermediate and to carry out postmodification of natural products.

Materials with low dielectric constant and loss and good thermal properties prepared by introducing perfluorononenyl pendant groups onto poly(ether ether ketone).

A new monomer, 2,6-difluorophenyl-(4'-perfluorononenyloxy)phenyl-methanone (2F-PFN), was synthesized using a simple two-step reaction. A series of novel poly(ether ether ketone)s (PEEK-PFN-x) containing perfluorononenyl groups were then prepared from 2F-PFN, resorcin, and 4,4'-difluorobenzophenone by nucleophilic polycondensation. The resulting copolymers were found to have different electric and thermal properties depending on the molar ratio of perfluorononenyl groups. PEEK containing a 5% molar ratio of perfluorononenyl (PEEK-PFN-5) possessed an intrinsic low dielectric constant of 2.73 and low dielectric loss of 3.00 × 10-3 at 10 kHz. Another blended polymer prepared from PEEK and PTFE (PEEK/PTFE-5) possessed a dielectric constant of 3.21 and dielectric loss of 6.00 × 10-3 at 10 kHz. Therefore, PEEK/PTFE-5 had much higher dielectric loss than that of PEEK-PFN-5 with the same fluorine content. PEEK-PFN-5 also showed excellent thermal stability, with a 5 wt%-loss temperature of 436 °C. PEEK-PFN-5 showed a slight increase in hydrophobicity, with a water droplet contact angle of 89.7° compared with that of PEEK/PTFE-5 (86.4°) containing the same fluorine content as PEEK-PFN-5. Morphologies and fluoride distribution on the membrane surfaces were characterized by field emission SEM equipped with EDX. These results indicated that PEEK-PFN-5 possessed a more uniform distribution of fluorine on the membrane top surface than PEEK-PTFE-5.

Correction: Materials with low dielectric constant and loss and good thermal properties prepared by introducing perfluorononenyl pendant groups onto poly(ether ether ketone).

[This corrects the article DOI: 10.1039/C7RA13600E.].