DFT study of the 1,3‐dipolar cycloaddition of azomethine ylides with maleimide,maleic anhydride,methylacrylate and some simple substituted alkenes

DFT calculations involving the B3LYP functional and 6‐31G(d) basis set have been performed to rationalize the reactivity, regioselectivity, enantioselectivity and diasteriofacial selectivity in the context of 1,3‐dipolar cycloaddition (13DC) reactions of a few acyclic and two cyclic azomethine ylides (AY) leading to enantiomeric/ diasteriomeric excess of the products. In particular, N‐substituted and C‐substituted AYs have been considered for reactions with the substituted ethylenes, maleimide, maleic anhydride and methyl acrylate. From an analysis of the results of calculation for the selected reactions, the regio‐ and exo/endo‐stereoselectivity have been explained. Reactions were followed through transition state (TS) structure optimization, calculation of IRC and activation energies. A rationalization of the trends in regioselectivity and enantioselectivity was attempted with the help of HOMO–LUMO energies, electrophilicity differences (Δω) and an analysis of Pauling's bond order (PBO) in the TS. Copyright © 2009 John Wiley & Sons, Ltd.     

Reactions on a 1,2-Dicarbonyl Moiety of a Fullerene Skeleton

A 1,2-dicarbonyl moiety on a cage-opened fullerene skeleton is one of suitable building blocks for the further derivatization. Herein, we discuss the chemical transformation of a 1,2-dicarbonyl compound into β-oxo-phosphorus ylide, acid anhydride, and α-methylene carbonyl derivatives. Despite possessing a sterically small methylene unit in the last one, the release of an encapsulated water molecule was significantly supressed whereas the β-oxo-phosphorus ylide bearing three bulky p-tolyl groups on the P-atom enabled the faster insertion/release dynamics, implying the flexibility of the phosphonium substituent. The replacement of the carbonyl group with phosphorus ylide and methylene units largely varied electrochemical properties of the fullerene skeleton, likely arising from the anionic charge delocalized over the entire molecule and removal of an electron-withdrawable carbonyl group, respectively.     

Alkene Synthesis by Photo-Wolff-Kischner Reaction of Sulfur Ylides and N-Tosylhydrazones

A visible-light-driven and room temperature photo-Wolff-Kischner reaction of sulfur ylides and N-tosylhydrazones has been developed for the first time to provide modular access to alkene synthesis. The high functional group tolerance and broad substrate scope were demonstrated by more than 60 examples. Both E- and Z-olefinic stereochemistry in the products could be controlled with excellent stereoselectivity. A series of mechanistic studies support that the reaction should proceed through a radical-carbanion crossover pathway, specifically involving addition of photo-generated sulfur ylide radical cations to N-tosylhydrazones to form carbanions and subsequent Wolff-Kischner process.     

Origins of the Reactivity in 1,3-Dipolar Cycloadditions of Acyl Isocyanide Ylides

1,3-Dipolar cycloadditions are the preferred method to generate five-membered heterocyclic rings. Surprisingly, cycloadditions based on acyl-isocyanide ylides have remained underexplored by the chemical community. Acyl-isocyanide ylides readily react with dipolarophiles, such as substituted alkenes, to yield Δ¹-pyrroline derivatives. As an explanation for the observed reactivity of this reaction is lacking, extensive density functional theory calculations were performed to scrutinize the mechanistic features of the transformation. Herein we explain the experimental outcome of the reaction using a variety of reactivity theories and predict opposed regioselectivity for electron-poor and electron-rich dipolarophiles. With the insights obtained, we hope to incentivize the design of new cycloaddition reactions based on the acyl-isocyanide ylides motif.     

Rh(III)-Catalyzed Annulative Coupling of Sulfoxonium Ylides with Allyl Acetates: Generation of Bicyclo[4.1.0]heptan-2-ones

A highly efficient Rhodium(III)-catalyzed annulative coupling was developed for generating bicyclo[4.1.0] heptan-2-ones from sulfoxonium ylides and allyl acetates under mild conditions. This cascade reaction is versatile to construct cyclopropanes, and the starting materials are stable and easily obtainable.