Cathodic reduction efficiently cleaved N–O bonds. The simple cathodic reduction of Weinreb amides in a divided cell afforded the corresponding amide in good yields. Cyclic voltammetry experiments and ...density functional theory calculations suggested that the direct reduction of the N-methoxy amide generates the methoxy radical and amide anion. The release of methanol derived from methoxy radical would be the driving force of the N–O bond cleavage.
We report the development of Pd(II)-catalyzed C(sp3)–H arylation of Weinreb amides. Both the inductive effect and the potential bidentate coordination mode of the Weinreb amides pose a unique ...challenge for this reaction development. A pyridinesulfonic acid ligand is designed to accommodate the weak, neutral-coordinating property of Weinreb amides by preserving the cationic character of Pd center through zwitterionic assembly of Pd/ligand complexes. Density functional theory (DFT) studies of the C–H cleavage step indicate that the superior reactivity of 3-pyridinesulfonic acid ligand, compared to Ac-Gly-OH and ligandless conditions, originates from the stabilization of overall substrate-bound Pd species.
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A cascade cyclization from Weinreb amide‐tethered methylenecyclopropanes and alkynes has been disclosed in this paper, which extends the umpolung ring opening of methylenecyclopropanes, giving a ...synthetic approach for the construction of polycyclic cyclopentabnaphthalenol framework. In the protocol, four carbon‐carbon bonds and two carbocycles are formed without the use of transition metals, providing a tool for constructing the structure‐related polycyclic compounds.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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•Novel 4,6-unsubstituted 5-acyl-2-phenyldihydropyrimidines were synthesized.•The combination of tetrahydropyrimidine and organolithiums is significant.•The two-step reactions gave the ...dihydropyrimidines in satisfactory yields.•Tautomerization of N-unsubstituted dihydropyrimidines was analyzed by 1H NMR.
A method of convergent and stepwise synthesis of novel 4,6-unsubstituted 5-acyl-2-phenyldihydropyrimidines using the Weinreb amide group is developed. The cyclization of 4-dimethylamino-1,3-diaza-1,3-butadiene having N-protecting groups (Boc) with N-methoxy-N-methylacrylamide gives 6-unsubstituted 4-dimethylamino-2-phenyltetrahydropyrimidine, which is a synthetic intermediate for 4,6-unsubstituted 5-acyl-2-phenyldihydropyrimidines. The transformation of the Weinreb amide group to an acyl group via substitution reaction using organolithium reagents, following the elimination of a dimethylamino group using MeI proceeds smoothly, affording 4,6-unsubstituted 5-acyl-2-phenyldihydropyrimidines in good overall yield. The N-protecting group can be easily removed to obtain N-unsubstituted dihydropyrimidines as a mixture of tautomers, and their tautomeric behaviors were analyzed by 1H NMR spectroscopy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The diastereoselective access to cyclopentanols and N,O‐dimethylcyclopentylhydroxylamines from 4‐pentenoic acid‐derived Weinreb amides is described. Based on the concomitant generation of both the ...nucleophilic and the electrophilic poles by hydrozirconation of the amide and the C=C double bond, the cyclisation may be tuned towards cyclopentanols or N,O‐dimethylcyclopentylhydroxylamines depending on the ring‐closure promotor. An extension to cis 3‐substituted N,O‐dimethylcyclohexylhydroxylamines is also presented.
The concomitant generation of a nucleophilic and an electrophilic site from unsaturated Weinreb amide by using Cp2Zr(H)Cl) as the unique reagent was developed to promote a cyclisation reaction. The access to trans‐2‐substituted cyclopentanols or cyclopentylhydroxylamines can be selectively driven by a judicious choice of the cyclisation promotor. An access to cis‐3‐substituted is also described.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
An efficient method for the direct synthesis of Weinreb amides derived from serine and threonine derivatives via diboronic acid anhydride-catalyzed hydroxy-directed amidation is described. ...This is the first successful example of the synthesis of serine- or threonine-derived Weinreb amides using catalytic dehydrative amidations. The methodology could be applied to the concise synthesis of Garner’s aldehyde.
α,β-Unsaturated esters were selectively protected in situ in the presence of α,β-unsaturated Weinreb amides using PEt3 and trimethylsilyl trifluoromethanesulfonate (TMSOTf) in toluene under reflux. ...Diisobutylaluminium hydride (DIBAL-H) reduction of the mixture followed by tetra-n-butylammonium fluoride (TBAF) treatment produced α,β-unsaturated aldehydes in good yields along with the recovered α,β-unsaturated esters.
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•Novel 4,6-unsubstituted 5-acyl-2-aminodihydropyrimidines were synthesized.•The Staudinger/aza-Wittig/cyclization reactions gave the synthetic intermediate.•The transformation of the ...Weinreb amide to an acyl group proceeded smoothly.•Tautomerization of N-unsubstituted dihydropyrimidines was analyzed by 1H NMR.
A method of convergent synthesis of novel 4,6-unsubstituted 5-acyl-2-aminodihydropyrimidines 7 is developed. The synthetic intermediate of 7, 4,6-unsubstituted 2-aminodihydropyrimidines 9 having a Weinreb amide at the 5-position, is prepared by the sequential Staudinger/aza-Wittig/cyclization reactions of (E)-tert-butyl{3-azido-2-methoxy(methyl)carbamoylallyl}carbamate (E)-10. The transformation of the Weinreb amide of 9 to an acyl group proceeds smoothly by a substitution reaction using aryllithiums or alkyllithiums in the presence of a catalytic amount of BF3 etherate, affording 7 in good to high yield. The N-protecting group of 7 can be easily removed to obtain N-unsubstituted 2-amino-5-acyldihydropyrimidines 8, and the derivatives are observed as a single isomer in 1H NMR spectroscopy. All dihydropyrimidines in this study were hitherto unavailable and difficult to synthesize by conventional methods.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
α,β-Unsaturated esters were selectively protected in situ in the presence of α,β-unsaturated Weinreb amides using PEt3 and trimethylsilyl trifluoromethanesulfonate (TMSOTf) in toluene under reflux. ...Diisobutylaluminium hydride (DIBAL-H) reduction of the mixture followed by tetra-n-butylammonium fluoride (TBAF) treatment produced α,β-unsaturated aldehydes in good yields along with the recovered α,β-unsaturated esters.
Various optically active 2-hydroxyamide derivatives are produced based on the kinetic resolution of racemic 2-hydroxyamides with a diphenylacetyl component and (
)-benzotetramisole ((
)-BTM), a ...chiral acyl-transfer catalyst, via asymmetric esterification and acylation. It was revealed that a tertiary amide can be used with this novel protocol to achieve high selectivity (22 examples;
-value reaching over 250). The resulting chiral compounds could be transformed into other useful structures while maintaining their chirality.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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