Cycloaddition Reaction Of Aldehydes Research Articles

Highly selective intermolecular one-pot three component 1,3-dipolar cycloaddition reaction of aldehydes, with phosphonates and proline

The use of l-proline to act as an organocatalyst in the aldol reaction of acylphosphonates and non enolizable aldehydes failed; however, it reacted with the aldehydes to afford azomethine ylides after decarboxylation that in turn underwent 1,3-dipolar cycloaddition with the acylphosphonates to form a bicyclic hexahydropyrrolo[1,2-c]oxazol-1-ylphosphonates in good yield. No azomethine ylide formation was observed on the reaction of acylphosphonates with proline.

ChemInform Abstract: Lewis Acid Promoted Hetero [2 + 2] Cycloaddition Reactions of Aldehydes with 10-Propynyl-9(10H)-acridone. A Highly Stereoselective Synthesis of Acrylic Acid Derivatives and 1,3-Dienes Using an Electron Deficient Variant of Ynamine.

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Mechanism for Cyclization Reaction by Clavaminic Acid Synthase. Insights from Modeling Studies

The mechanism of the oxidative cyclization reaction catalyzed by clavaminic acid synthase (CAS) was studied in silico. First, a classical molecular dynamics (MD) simulation was performed to obtain a realistic structure of the CAS-Fe(IV)=O-succinate-substrate complex; then potential of mean force (PMF) was calculated to assess the feasibility of the beta-lactam ring, more specifically its C4' corner, approaching the oxo atom. Based on the MD structure, a relatively large model of the active site region was selected and used in the B3LYP investigation of the reaction mechanism. The computational results suggest that once the oxoferryl species is formed, the oxidative cyclization catalyzed by CAS most likely involves either a mechanism involving C4'(S)-H bond cleavage of the monocyclic beta-lactam ring, or a biosynthetically unprecedented mechanism comprising (1) oxidation of the hydroxyl group of PCA to an O-radical, (2) retro-aldol-like decomposition of the O-radical to an aldehyde and a C-centered radical, which is stabilized by the captodative effect, (3) abstraction of a hydrogen atom from the C4'(S) position of the C-centered radical by the Fe(III)-OH species yielding an azomethine ylide, and (4) 1,3-dipolar cycloaddition to the ylide with aldehyde acting as a dipolarophile. Precedent for the new proposed mechanism comes from the reported synthesis of oxapenams via 1,3-dipolar cycloaddition reactions of aldehydes and ketones.

Lewis Acid Promoted Hetero [2 + 2] Cycloaddition Reactions of Aldehydes with 10-Propynyl-9(10H)-acridone. A Highly Stereoselective Synthesis of Acrylic Acid Derivatives and 1,3-Dienes Using an Electron Deficient Variant of Ynamine

Reactivities of 10-propynyl-9(10H)-acridone toward various aldehydes in BF3·Et2O-promoted hetero [2 + 2] cycloaddition reactions are described here. This electron deficient variant of ynamine is more stable and easier to handle than most ynamines but possesses comparable reactivity. These reactions lead to a highly stereoselective synthesis of trisubstituted alkenes. A mechanistic model based on the stereochemical assignment is also described here. 10-Propynyl-9(10H)-acridone is also reactive toward α,β-unsaturated aldehydes and ketones. It provides hetero [2 + 2] products in reactions with α,β-unsaturated aldehydes but gives only the inverse demand [4 + 2] cycloadduct in a reaction with methyl vinyl ketone.

Catalytic and substituent effects on cycloaddition reactions between isocyanates and aldehydes

The cycloaddition reactions of aldehydes and isocyanates leading to 1-oxo-3-azetidine-2-ones were studied theoretically. For the model reaction(HNCO+H 2CO) and the catalytic reaction(HNCO+H 2CO…BH 3), the stationary points are located by HF/6-31G*, MP2/6-31G* and MP2/6-31++G** respectively. IRC calculation, at HF/6-31G* level, showed that this type of reaction is concerted. Four frontier orbitals are involved in these reactions, which are of `2×[1+1]' type. The parent reaction has a 34.0 kcal/mol energy barrier at the MP2/6-31++G** level; while the BH 3-catalyzed reaction has one at 18.1 kcal/mol. The presence of different substituted groups on isocyanates and/or on aldehydes will change energies as well as the structures of transition states, but all the studied reactions are believed to be concerted. The calculations also show that the substitution of the F or SO 2Cl group on isocyanate and/or CF 3 groups on aldehyde will favor the reaction. The reaction FNCO+PhCHO is the easiest among our studied reactions.