5014-83-5Relevant articles and documents
(Enantio)selective Hydrogen Autotransfer: Ruthenium-Catalyzed Synthesis of Oxazolidin-2-ones from Urea and Diols
Pe?a-López, Miguel,Neumann, Helfried,Beller, Matthias
supporting information, p. 7826 - 7830 (2016/07/07)
A novel strategy for the synthesis of oxazolidin-2-ones from vicinal diols and urea is described. In this heterocycle synthesis, two different C?O and C?N bonds are sequentially formed in a domino process consisting of nucleophilic substitution and alcohol amination. The use of readily available starting materials and the good atom economy render this process environmentally benign. While this transformation is already highly chemo- and regioselective, we also developed the first asymmetric version of this method using (R)-(+)-MeO-BIPHEP as the chiral ligand.
Substituted Oxazoles: Synthesis via Lithio Intermediates
Whitney, Scott E.,Rickborn, Bruce
, p. 3058 - 3063 (2007/10/02)
Reactions of 2-α-, 2-, 4-, and 5-lithiooxazoles are used to prepare various substituted derivatives.Previously unrecognized time dependence for the reaction of a 2-lithiooxazole with benzaldhyde is described, and a rationale for this behavior is offered.Competitive reactions occur when the readily available 2,5-diphenyloxazole is treated with n-butyllithium.Deprotonation of the ortho position of the 2-phenyl group and addition of n-butyl to the 2-position of the oxazole compete with the desired 4-lithiation.The use of sec-butyllithium/catalytic lithium tetramethylpiperidide allows preferential formation of 4-lithio-2,5-diphenyloxazole.This intermediate has been converted to the 4-bromo, -methyl, -hydroxybenzyl, -benzoyl, and -trialkylsilyl derivatives.Lithiation of 2,4-diphenyloxazole and subsequent trimethylsilylation occur readily at the 5-position.Deprotonation of 2-alkyloxazoles occurs at the α-carbon in preference to ring sites.Further reaction of an α-phenyl-2-oxazolemethanol methoxymethyl ether with base and acetyl chloride leads to an acyloin derivative.Chromic acid oxidation is used to prepare both 2- and 4-benzoyloxazoles.The formation of an 2-ethoxyoxazole from 2-oxazolone vis Meerwein salt chemistry is described.
Synthesis of α,β-Epoxyacyl Azides and Their Rearrangement to Epoxy Isocyanates and 3- and 4-Oxazolin-2-ones
Lemmens, Jacques M.,Blommerde, Willem W. J. M.,Thijs, Lambertus,Zwanenburg, Binne
, p. 2231 - 2235 (2007/10/02)
The conversion of α,β-epoxy carboxylates 6 into α,β-epoxyacyl azides 4 proceeds either via reaction of the mixed anhydrides 7 with sodium azide or via reaction of epoxyacyl chlorides 8 with hydrazoic acid-pyridine.The latter method is preferred.The azides 4 undergo a smooth thermal Curtius rearrangement to give 4-oxazolin-2-ones 10 for the substrates 4a-h having a hydrogen atom at C(β).Monitoring this reaction by means of IR shows that the epoxy isocyanates 5 are intermediates.Intramolecular ring expansion of 5 then leads to 3-oxazolin-2-ones 9 that tautomerizeto the 4-isomers 10a-h.Epoxyacyl azides 4i,n-q, having no hydrogen atom at C(β), producing 3-oxazolin-2-ones 9i,n-q by a proton shift is not possible.The products 9i and 9q rapidly add water at the imine bond to give oxazolidin-2-ones 11.Epoxy isocyanate 5k is reasonable stable in solution; reaction with methanol affords urethane 12.
