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Communication | Regular issue | Vol 89, No. 3, 2014, pp.631-639
Published online, 30th January, 2014
DOI: 10.3987/COM-14-12941
■ Enantioselective Intramolecular Aza-Spiroannulation onto Benzofurans Using Chiral Rhodium Catalysis

Takuro Shibuta, Shigeki Sato, Masatoshi Shibuya, Naoki Kanoh, Tohru Taniguchi, Kenji Monde, and Yoshiharu Iwabuchi*

*Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aobayama, Sendai 980-8578, Japan

Abstract

The development of efficient and enantioselective intramolecular aza-spiroannulation onto benzofurans using chiral rhodium catalysis is described. The optimized reaction conditions [Rh2(S-TCPTAD)4 (3 mol %), PhIO (1.6 equiv), MeOH (10 equiv) in PhCF3, 0 °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).