Cs2co3, catalyzed the cycloaddition reaction of ketene 2a. With acetone, ketene reacts to give isopropenyl acetate. Methyl ketene generates two dimers, one with a lactone structure and the other having a cyclopbutandione structure. Rapid communications in mass spectrometry 1993, 7 1, 9598. Enantioselective synthesis of betatrifluoromethylbeta. Ketene chemistry and the application in synthesis dong group at ut austin xuan zhou nov 14, 20. Ketenes are reactive compounds that dimerize to diketenes.
It is a pericyclic chemical reaction where two or more unsaturated molecules or parts of the same molecule combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity. The diastereoselection of the cycloaddition process can be controlled with variable success from chiral groups attached to either the ketene or the imine component, or alternatively to both. Ketenes may react with unsaturated compounds to afford fourmembered or larger rings. Some of the keteneimine cycloaddition reactions used for the synthesis of 1,4. Solvent effects on structure and reaction mechanism. Apr 29, 2011 the cycloaddition afforded a carbocyclic product 1a that resulted from the coupling of the cc bond of ketene a rather than a pyran 1a, which would have resulted from the coupling of the co bond. These reactions may be performed in hydroxylic solvents, supporting. It is known that this type of 1,3rearrangement of allylic esters is promoted by pd 0 and pd ii complexes.
Catalytic asymmetric acyl halidealdehyde cyclocondensation. To the best of our knowledge, the investigations of dimerization reactions of alkyl ketene are mainly focused on. Ketene chemistry content a brief history of ketene. Mechanism of cycloaddition reactions between ketene and nsilyl, ngermyl, and nstannylimines. Aug 29, 2017 in cycloaddition reactions with unsaturated compounds, diazo compounds are directly utilized as nn or nnctype dipolar components. However, to the best of our knowledge, the detail information about the reaction mechanism and its stereo and regioselectivity have not been obtained yet. It is of significant importance to research the cycloaddition reaction mechanism of alkyl ketene for the synthesis of akd and the rich chemical theories. Synthesis and claisen rearrangement of bridged bicyclic.
It is one of the most widely used methods for the synthesis of azetidin2ones due to the availability of plentiful and a variety of sources. Regioselectivity regioselectivity for the reaction of ketene with alkene can be predicted using the ionic approach and taking into consideration that the carbonyl carbon of ketenes is very electrophilic or by using orbital coefficients approach. Keywords lactams, ketene, imine, staudinger reaction, ketene imine cycloaddition, ab initio calculations. Despite this, the detailed mechanism of this reaction.
The ketene imine cycloaddition reactions, developed previously by the nelson group, have been extended to the intramolecular ketene imine cycloaddition. The relative small size of ketene and imine allows more accurate levels of ab initio. If the product of a cycloaddition of ketene itself is desired, dichloroketene is typically used, followed by dehalogenation with zinccopper couple. Examples of all three modes of cycloaddition are discussed in this section. Highly efficient ketal cleavage to either 2cyano1cyclobutanone or 2.
Mar 29, 2021 the synthetic importance of these reactions is very great and, because many of them often involve dienes, we will discuss their general characteristics in this chapter. Cycloaddition reactions and sigmatropic rearrangements both involve pairs of. First published on unassignedunassigned7th january 2000. Staudinger ketene cycloaddition an overview sciencedirect topics. Additional evidence for the existence of this adduct was obtained from its c nmr spectrum. The results show that the acetylpyridines react with an electron rich, dimethylsubstituted silyl ketene acetal via a pathway in which excited state single electron transfer set takes place to prod. Both the ketene and the imine are molecules that can act as either nucleophiles or electrophiles.
Research article theoretical research on the mechanism of. On the other hand, only intermolecular reactions of ketene styrene cycloaddition, where the substituted styrenes. Photoaddition reactions of acetylpyridines with silyl ketene. Reactions of ketenes cycloaddition ketenes with imines form. The journal of physical chemistry a 2005, 109 48, 1102211026. Intramolecular ketene imine cycloadditionthe ketene imine cycloaddition reactions, developed previously by the nelson group, have beenextended to the intramolecular cycloaddition of the ketene imine cycloaddition. Mechanism of cycloaddition reactions between ketene and n. Ketenes react with alkenes to provide cyclobutanones. Asymmetric synthesis of lactams by staudinger ketene.
Oct 15, 2004 ketene cycloaddition was an early example of a peculiar process, one that formed carboncarbon bonds with ease, often without the need for solvent, catalyst, or high heat. Sep, 2020 the most common cycloaddition reaction is the 4. Research article theoretical research on the mechanism of the. To the best of our knowledge, the investigations of dimerization reactions of alkyl ketene are mainly focused on experimental study and rarely on theoretical study , 14. Cycloaddition simple english wikipedia, the free encyclopedia.
Photoaddition reactions of acetylpyridines with silyl. Cycloaddition reactions in organic synthesis, volume 8 1st. It is of signi cant importance to research the cycloaddition reaction mechanism of alkyl ketene for the synthesis of akd and the rich chemical theories. Some ketenes such as ethenone dimerize, forming a lactone oxetan2one. The formation of the two possible dimers is shown in the following reaction. Cycloaddition reactions between cyclopentadiene and ketene. Initial resultsshowed that the intramolecular cycloaddition exhibited excellent enantioselectivity, but it wassuffered from poor diastereoselectivity. Imine cycloaddition reactions, cheminform on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Cycloaddition reactions of acyl ketenes home thieme connect. A caspt2 and casscf approach to the cycloaddition of ketene. The reaction of ketene with itself was described almost simultaneously in 1908 by chick and wilsmore in england, and by staudinger and klever in germany. In these reactions the ketene is fully generated prior to addition of alkene and lewis acid. A cycloaddition is a chemical reaction between reactants with double bonds that get replaced by a ring structure.
If all the bonding events take place on the same face of the. The key step in the asymmetric synthesis utilised a modena asymmetric oxidation of 2benzyloxymethyl1,3dithiolane which gave the trans bissulfoxide with high diastereocontrol 91. The results show that the acetylpyridines react with an electron rich, dimethylsubstituted silyl ketene acetal via a pathway in which excited state single electron transfer set takes place to. Staudinger ketene imine cycloaddition uncatalyzed mechanism. Theoretical research on the mechanism of the dimerization. A caspt2 and casscf approach to the cycloaddition of. Ab initio study on the mechanism of cycloaddition reaction of ketene with methylenimine. Ketenes and ketene s,sacetals displace ethylene from ptpph 3 2 c 2 h 4 to form. The periselectivity of a particular reaction depends on the structure of both the ketene and the substrate. Staudinger ketene cycloaddition an overview sciencedirect. A theoretical study on the reaction mechanisms and. The zwitterionic intermediate undergoes stepwise ring closure to give the. Jan 20, 2007 read mechanistic aspects of the keteneimine cycloaddition reactions, cheminform on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Mcscf study of the cycloaddition reaction between ketene and.
Photoaddition reactions of silyl ketene acetals with 2, 3 and 4acetylpyridine have been explored. This is the staudinger synthesis, a facile route to this important class of compounds. Claisen rearrangement of these substrates either thermally or in the presence of an added lewis acid results in the formation of bicyclic cyclobutanones with generally good conversions. To extend the utility of this method towards use of unstable ketenes, like. Cycloaddition reactions of ketene diethyl acetal toward. Theoretical study of the electronic effects in the. Instead a previously unreported reaction took place with nmethyl aryl imines. Subsequent work by others was done in the shadow of staudingers exhaustive and rigorous study of all phases of ketene reactivity.
Cycloaddition reactions of ketene diethyl acetal toward the. Cycloaddition reactions ketene cycloadditions youtube. The author, a leading exponent of the subject, illustrates the ways in which they can be employed in the synthesis of a wide range of carbocyclic and heterocyclic. Ketene cycloaddition was an early example of a peculiar process, one that formed carboncarbon bonds with ease, often without the need for solvent, catalyst, or high heat. Some of the ketene imine cycloaddition reactions used for the synthesis of 1,4 diaryl azetidin2ones are listed below. Cycloaddition reactions in organic synthesis, volume 8. The synthesis is described of a range of 3alkylidene2oxabicyclo2. The first example of this phenomenon was observed in 1908, and since then, cycloadditions of ketenes have expanded and gained synthetic utility. Efforts to form an adduct with tertbutyl cyano ketene and sulfur dioxide, analogous to 15, were unsuccessful. The relative small size of ketene and imine allows more accurate levels of.
Regioselectivity for the reaction of ketene with alkene can be predicted using the ionic approach and taking into consideration that the carbonyl carbon of ketenes is very electrophilic or by using orbital coefficients approach. Dimerization of the ketene cation radical in the gas phase. Pdf a theoretical study on keteneolefin cycloadditions. Claudio palomo, jesus maria aizpurua, asymmetric synthesis of 3amino.
Sep 17, 2009 enantioselective synthesis of betatrifluoromethylbetalactones via nhccatalyzed ketene ketone cycloaddition reactions. In dielsalder terminology the two reactants are referred to as the diene and the dienophile. The thermal reaction of ketenes with olefins to form cyclobutanones is a. Lactams by staudinger ketene imine cycloaddition reaction claudio palomo,a jesus m. In the dimerization reaction, alkyl ketene always forms fourring compounds. Mechanistic aspects of the keteneimine cycloaddition. Dft study on the mechanisms and diastereoselectivities of. This method, in turn, has proved to be valuable for the synthesis of precursors of important lactam antibiotics, and new successful applications can. Ketenes, cycloadditions, reaction mechanisms, computations. Initial results showed that the intramolecular cycloaddition exhibited excellent enantioselectivity, but it was suffered from poor. In the first step, the imine adds to the ketene as a nucleophile.
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