In each case the diene reactant is colored blue, and the new. The reactions allows for the asymmetric synthesis of transhexahydroindenes and pyrrolidine products using c 3symmetric phosphitegoldi and orthoarylphosphoramiditegoldi complexes as catalysts, respectively. A protocol for the asymmetric synthesis of highly substituted chiral allenes with control of point and axial chirality has been developed. The structural integrity of 6a and 6b was determined through hh cosy and noe experiments. Higher order cycloadditions in synthesis group meeting o. Read cycloaddition of heterofunctionalized allenes with tert. Lawrence n n o h dactylol sarain a me me me meh ho o ome ome meo meo. The computed free energy surface is shown in figure figure3. In dielsalder terminology the two reactants are referred to as the diene and the dienophile. Recent developments in cyclopropane cycloaddition reactions. The dielsalder reaction is perhaps the most important and commonly taught cycloaddition reaction. Cycloaddition reactions, by involving the formation of at least two bonds and one cycle in a single operation, represent one of the more practical ways to assemble carbo and heterocyclic. May 16, 2011 cycloaddition reactions are among the synthetic tools that best fit these criteria, because by allowing the generation of at least two bonds and one cycle in a single operation, they produce a rapid increase in skeletal and also stereochemical complexity, and this is usually beneficial in terms of shortening the access to polycyclic products. Ketenes, unlike most alkenes, can align antarafacially with respect to other alkenes.
Chemistry electron structures in atoms 7 of 40 photochemical reaction duration. Cycloaddition reactions are among the synthetic tools that best fit these criteria, because by allowing the generation of at least two bonds and one cycle in a single operation, they produce a rapid increase in skeletal and also stereochemical complexity, and this is usually beneficial in terms of shortening the access to polycyclic products. Icatalyzed intramolecular 3 2 cycloaddition of 1allene. It represents one of the relatively few synthetic methods available to form sevenmembered rings stereoselectively in high yield. Studies on the himbert intramolecular arene allene diels. By contrast, the synthesis of larger rings through higher order cycloaddition reactions is far less common.
A cycloaddition is a chemical reaction, in which 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. Cycloadditions in organic synthesis introduction 2 cycloaddition describes the union of two independent. Carruthers, cycloaddition reactions in organic synthesis, ch. Allenes in total synthesis the anderson research group. Cycloaddition reactions are considered among the most powerful. Determination of activation parameters for diradical intermediate formation and the detection of reversible ring closure, journal of physical organic chemistry on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Cycloaddition reactions results in the formation of a new ring. Synthesis of first chiral allene, maitland and mills, nature 1935, 994. The cycloaddition reaction of a neutral allene only with steric bias, 5b yielded a similar result to the reaction of 5a as a diastereomeric mixture of 6b was obtained. Jul 11, 2014 for the love of physics walter lewin may 16, 2011 duration.
The interaction of a sulfamate ester derived metallonitrene with an allene generates a versatile intermediate with 2amidoallylcation like reactivity. Cycloaddition of heterofunctionalized allenes with tert. Xiaolei gong, wenchao gao, honghong chang, wenlong wei, xing li department of biological and pharmaceutical engineering, college of chemistry and chemical engineering, taiyuan university of technology, taiyuan 030024, china. A new allenic pausonkhand cycloaddition for the preparation.
Cycloadditions of allenes and the application in natural product syntheses. Allenes in total synthesis mohammad mujahid eaa group, university of oxford 2nd june 2016. Cycloaddition, electrocyclic, sigmatropic, and ene reactions. Reactivity and chemoselectivity of allenes in rhicatalyzed. Goldicatalyzed enantioselective cycloaddition reactions. Dielsalder reactions of allene with benzene and butadiene. May 15, 20 himbert and coworkers were the first to discover and study the scope of the intramolecular areneallene cycloaddition reactions 1,2 and, on the basis of the relative insensitivity of cycloaddition rates to donor and acceptor groups on the arene in amidetethered substrates, they were led to favor a concerted cycloaddition mechanism over a. This strategy has been widely studied under thermal, photochemical and microwave induced conditions. Himbert and coworkers were the first to discover and study the scope of the intramolecular areneallene cycloaddition reactions 1,2 and, on the basis of the relative insensitivity of cycloaddition rates to donor and acceptor groups on the arene in amidetethered substrates, they were led to favor a concerted cycloaddition mechanism over a. Sharpless in 2001 to describe reactions that are high yielding, wide in scope, create only byproducts that can be removed without chromatography, are stereospecific, simple to perform, and can be conducted in easily removable or benign solvents. The cycloadditions are chemoselective as only the proximal double bond of the allene reacted to afford exocyclic double bonds in the fused. Particular attention has been paid during the last years to the development of enantioselective versions of these processes by.
The four principle classes of pericyclic reactions are termed. The research in cycloaddition reactions of allenic compounds. Kent department of chemistry, west virginia university morgantown, west virginia 26506 a new stereoand regioselective method for the preparation of. A series of cyclopropanerelated cycloaddition reactions via organic or metalcatalyzedmediated pathways has been. Many but not all cycloadditions are concerted and thus pericyclic. Differentiating mechanistic possibilities for the thermal.
Molecules with chiral axis leading to extended tetrahedral shape. Allenes are known to be moderately reactive toward cycloaddition reactions. Phosphinecatalyzed annulations of azomethine imines. Dec 10, 2014 reactions with dimethylsubstituted allene. It is commonplace for researchers to postulate diradical intermediates for thermally disallowed cycloaddition reactions, but rarely are experiments conducted to support their existence. Cycloaddition reactions offer a versatile route for the synthesis of cyclic compounds with a high degree of stereoselectivity under thermal and photochemical conditions. Due to the breadth of this topic, this presentation is far. Two sigma and two pi bonds with central c being sphybridised. Cycloadditions of allenes and the application in natural product syntheses dong group at ut austin xuan zhou nov 12, 2014. Cycloaddition reactions jiaxin liu, 1ruixing liu, yin wei,1 and min shi,2 in organic synthesis, the synthetic methodology of using cyclopropanes for cycloadditions has witnessed signi. Intramolecular cycloaddition reactions of allylic cations, michael harmata, tetrahedron, 53, 6235 1997. Cycloadditions of allenes and the application in natural. Higher order cycloadditions in synthesis group meeting omalley. Allenes are inherently chiral and can be prepared in optically pure form.
Thus, we will present cycloaddition processes i with a goldcarbene intermediate, ii involving an allene activation to generate a goldallyl cationic. Compounds containing allenes, cumulenes and oligoynes polyalkynes have attracted attention for. The allene cycloaddition reactions obey the woodward. Subjection of to a variety of cycloaddition conditions indeed. Since reactions of this kind often proceed by nearly simultaneous reorganization of bonding electron pairs by way of cyclic transition states, they have been termed pericyclic reactions. Click chemistry azidealkyne cycloaddition click chemistry is a term that was introduced by k. These reactions can be conducted with a variety of substrate substitution patterns and functional groups and often in the absence of solvent. Commonly employed allene equivalent, vinyl phosphonium salt. The mechanism of this reaction was examined computationally in collaboration with dean tantillo and matthew siebert and experimentally in our lab. These reactions consist of the addition of a system of p. Chapter 2 sets out the general objectives of the thesis. Alder reactions of alkene and alkyne dienophiles,17 we have undertaken a. A chiral auxiliary is a homochiral group that is temporarily directly attached to an achiral substrate rx. For the love of physics walter lewin may 16, 2011 duration.
It is widely accepted that, in the phosphinepromoted reactions of. 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. Cycloadditions of allenes and the application in natural product. Recent developments in goldcatalyzed cycloaddition reactions. Two complementary catalyst systems have been developed. Cycloaddition reactions are considered among the most powerful bondforming reactions in organic synthesis because of their ability to form many bonds in one step and also for their potential in generating several stereogenic centres at the same time with predictable stereochemical outcomes.
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