Enantioselective Intramolecular Aza-Spiroannulation onto Benzofurans Using Chiral Rhodium Catalysis
作者:Yoshiharu Iwabuchi、Takuro Shibuta、Shigeki Sato、Masatoshi Shibuya、Naoki Kanoh、Tohru Taniguchi、Kenji Monde
DOI:10.3987/com-14-12941
日期:——
The development of efficient and enantioselective intramolecular aza-spiroannulation onto benzofurans using chiral rhodium catalysis is described. The optimized reaction conditions [Rh-2(S-TCPTAD)(4) (3 mol %), PhIO (1.6 equiv), MeOH (10 equiv) in PhCF3, 0 degrees C] brought about oxidative aza-spiroannulation of 3-(carbamoylmethyl)benzofuran (3) resulting in (2R,3S)-2-methoxy-2H-spiro-[benzofuran-3,4'-oxazolidin]-2'-one (15a) in 69% yield with 86% ee, the absolute structure of which was determined by a combination of X-ray crystallography and vibrational circular dichroism (VCD) spectroscopy. The reaction is applicable to the asymmetric construction of various 2,3-dihydrobenzofuran derivatives bearing a nitrogen-containing tetrasubstituted carbon stereocenter at C3 (up to 92% ee).
Rhodium(II)-Catalyzed Aziridination of Allyl-Substituted Sulfonamides and Carbamates
作者:Albert Padwa、Andrew C. Flick、Carolyn A. Leverett、Thomas Stengel
DOI:10.1021/jo048990k
日期:2004.9.1
products in high yield. In contrast, the intramolecular aziridination of several cycloalkenyl-substituted carbamates did not require a Rh(II) catalyst and proceeded via an iminoiodinane intermediate. The resulting tricyclic aziridines underwent ring opening when treated with various nucleophiles to give anti-derived products as expected for nucleophilicattack at the three-membered ring. The iodine(III)-mediated