The base-catalysed Tamura cycloaddition reaction: Calculation, mechanism, isolation of intermediates and asymmetric catalysis
A combined experimental and computational investigation has revealed that the base-catalysed Tamura cycloaddition between homophthalic anhydride and activated alkenes/alkynes-a reaction previously thought of as a Diels-Alder type process-proceeds via a stepwise mechanism involving conjugate addition and ring closure; which allowed the first catalytic asymmetric α-substitution reactions to be demonstrated with up to >99% ee.
Lockett-Walters, Bruce,Trujillo, Cristina,Twamley, Brendan,Connon, Stephen
Organocatalytic cascade Michael/Michael reaction for the asymmetric synthesis of spirooxindoles containing five contiguous stereocenters
A bifunctional squaramide-catalyzed Michael/Michael cascade reaction for the construction of five-membered spirooxindoles was developed. This reaction afforded the corresponding products with five contiguous stereocenters including a quaternary center in good to excellent yields (up to 93%) with excellent stereoselectivities (up to >99-1 dr, 98% ee). Meanwhile, the practicality of this methodology was illustrated by a gram-scale synthesis, one-pot four-component reaction and synthetic transformation of the resulting adduct.
Benzylidene succinimides as 3C synthons for the asymmetric tandem Mannich reaction/transamidation of cyclic trifluoromethyl ketimines to obtain F3C-containing polycyclic dihydroquinazolinones
By taking advantage of benzylidene succinimides as a new class of 3C synthons, a highly diastereo- and enantioselective tandem Mannich reaction/transamidation has been established by reacting them with cyclic trifluoromethylN-acyl ketimines. Using aCinchonaalkaloid-derived squaramide as the catalyst, the tandem reaction proceeded smoothly under mild conditions and afforded a range of F3C-containing chiral polycyclic dihydroquinazolinones with excellent results (up to 99% yield, all cases >20?:?1 dr, up to 99% ee).
Indium-Catalyzed Amide Allylation of N-Carbonyl Imides: Formation of Azaspiro-γ-lactones via Ring Opening-Reclosure
A novel and facile synthesis of azaspiro-γ-lactones with a methylene-lactam framework from N-carbonyl imides is described. Mechanistic investigations provide evidence for a two-step reaction process involving ZnCl2-promoted addition of β-amido allylindium species followed by an unexpectedly molecular-sieves-mediated ring opening-reclosure concomitantly with the loss of an N-carbonyl unit.
Process for producing N-tertiary butoxycarbonyl-maleinimide
To produce N-tertiary butoxycarbonyl-maleinimide, maleinimide is reacted in the presence of a heterocyclic nitrogen compound having at least one tertiary nitrogen atom (as a base) with a more or less equimolar quantity of di-tertiary butyl-dicarbonate in a suitable solvent at temperatures of up to about 80° C.
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(2008/06/13)
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