Procedure-Controlled Enantioselectivity Switch in Organocatalytic 2-Oxazolidinone Synthesis

Abstract

In a novel organocatalytic formal [3 + 2] cycloaddition to afford chiral 2-oxazolidinones, an enantioselectivity switch could be induced by changing the manner of addition of the reactants, even when the reaction components (cinchona-alkaloid-derived aminothiourea catalyst, substrates, and solvent) were the same.

Organocatalytic Morita–Baylis–Hillman/Michael/Acetalization Cascade: Procedure‐Controlled Diastereodivergence in the Asymmetric Synthesis of Fully Substituted Tetrahydropyrans

“…NMR data was obtained for 1 H at 400 MHz, and for 13 C at 100 MHz. Chemical shifts were reported in ppm from tetramethylsilane with the solvent resonance as the internal standard in CDCl 3 solution.…”

“…Adding electron-withdrawing substituents to the aryl group generated the unreacted intermediate (S)-3b-3j with high enantioselectivity and the products 5b-5j in satisfying yield. Adding an electron-donating substituent to the aryl group, regardless of its position, led to a relatively low ee of the kinetic products and low yield of cycloaddition products (entries [11][12][13]. We were pleased to find that heteroaryl or alkyl nitroalkenes also reacted well under our optimized conditions, generating products 5n-5p in high yields but with moderate dr values.…”

“…If successful, this approach would provide an alternative method for the preparation of chiral tetrahydropyrans and a powerful demonstration of procedure-controlled diastereodivergence in asymmetric synthesis. [13] It would also broaden the useful scope of sequential dual catalysis [14] and organocatalytic cascade reactions. [15] To probe the feasibility of the proposed cascade process, preliminary experiments were performed using nitrostyrene 1a, ethyl glyoxylate 2a and propanal 4a as the standard substrates.…”

(Enantio)selective Hydrogen Autotransfer: Ruthenium‐Catalyzed Synthesis of Oxazolidin‐2‐ones from Urea and Diols

“…Based on previous studies by our group, [10] we initially used [Ru 3 (CO) 12 ]asthe catalyst in combination with different phosphines.O nly traces of the desired product were observed under ligand-free conditions,w hereas the use of different mono-and bidentate phosphines afforded 4-phenyloxazolidin-2-one (3a)s electively in moderate yields (20-52 %). Based on these first results,weperformed am ore detailed optimization of the best ligand system (dppf = 1,1'-bis(diphenylphosphino)ferrocene).…”

“…[a] Unless otherwise specified, all reactions were carried out with 1 (1.0 mmol), 2 (0.5 mmol), Ru 3 (CO) 12 medium also promotes further side reactions;therefore,h igher amounts of urea were required to achieve acceptable yields.N ext, we performed the reaction with carbamates as urea analogues.T he reaction of 2a with 5a-5d provided the heterocycle 3a in good yields (62-72 %; entries [13][14][15][16]. Here,the alcohol resulting from substitution does not participate in undesired reactions that decrease the yield.…”