Diastereoselective Access to Chiral Non‐racemic [1,3]Oxazolo[2,3‐a]isoindol‐5‐one Ring Systems via O‐Cationic Cyclization.

Abstract

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Diastereoselective Synthesis of Oxazoloisoindolinones via Cascade Pd-Catalyzed ortho-Acylation of N-Benzoyl α-Amino Acid Derivatives and Subsequent Double Intramolecular Cyclizations

“…The structures of the obtained products 3 were identified by 1 H NMR, 13 C NMR, and HRMS. Particularly, all products 3 were formed as a single diastereoisomer by the analyses of their 1 H NMR spectra.…”

“…H NMR chemical shifts were determined relative to internal TMS at δ 0.0 ppm. 13 C NMR chemical shifts were determined relative to CDCl 3 at δ 77.16 ppm. Data for 1 H NMR and 13 C NMR are reported as follows: chemical shift (δ, ppm) and multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, and m = multiplet).…”

“…13 C NMR chemical shifts were determined relative to CDCl 3 at δ 77.16 ppm. Data for 1 H NMR and 13 C NMR are reported as follows: chemical shift (δ, ppm) and multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, and m = multiplet). High-resolution mass spectra (HRMS) were measured with FTMS-ESI or TOF-ESI in positive mode on a LTQ-Orbitrap or Q-TOF mass spectrometer.…”

“…1 H NMR (400 MHz, CDCl 3 , δ): 7.82 (d, J = 8.5 Hz, 1H), 7.52−7.46 (m, 2H), 7.44− 7.37 (m, 3H), 7.07 (dd, J = 8.5, 1.9 Hz, 1H), 6.75 (d, J = 1.9 Hz, 1H), 4.18 (d, J = 9.7 Hz, 1H), 3.80 (s, 3H), 1.70−1.55 (m, 1H), 1.10 (d, J = 6.6 Hz, 3H), 0.90 (d, J = 6.6 Hz, 3H). 13 8-Fluoro-3-isopropyl-9b-phenyloxazolo[2,3-a]isoindole-2,5-(3H,9bH)-dione (3ma). By following the general procedure, the reaction of 1m (72.0 mg, 0.3 mmol) with 2a (90.3 mg, 0.6 mmol) at 70 °C for 12 h gave 3ma (82.0 mg, 84% yield).…”

“…12 Another approach is the intramolecular cationic cyclization with N-acyliminium species. 13 However, from a synthetic point of view, these methods suffer from some intrinsic drawbacks including poor functional group tolerance, harsh reaction conditions, bad stereoselectivity, and the requirement of prefunctionalization of the coupling partners. Therefore, it is highly desirable to develop novel and efficient protocols with fewer synthetic steps and better stereoselectivity for the synthesis of oxazoloisoindolinones.…”