Recent advances in asymmetric 3,3sigmatropic rearrangements. A novel 1, 3 sigmatropic rearrangement of ketene silyl acetals derived from benzyl. For example 3,4dimethyl1,5hexadiene heated to 300 c yields 2,6octadiene. The reaction proceeds through the formation of 2alkenyl1naphthalene thiols, which subsequently undergo cyclization to compounds of the 2,3dihydronaphtho1,2bthiophene and naphtho1,2bdihydrothiopyran series. The stereochemistry of the newly formed cc bond is harder to predict. Article pdf available in acta chemica scandinavica 505. It can be inferred from the fivemembered ring transition state. Table i where the migrating terminus has been either carbon or oxygen. Woodward and hoffmann defined a sigmatropic rearrangement of order i,j to be the.
Dietrich school of arts and sciences in partial fulfillment of the requirements for the degree of. Competitive pseudopericyclic 3, 3and 3, 5sigmatropic. The 3, 3 sigmatropic rearrangement of 1, 5dienes or allyl vinyl ethers, known. Oct 16, 2015 the cope rearrangement is an extensively studied organic reaction involving the 3,3 sigmatropic rearrangement of 1,5dienes. Although rare, there are examples where antarafacial shifts are favored. Claisen rearrangment of aryl allyl ethers university of calgary. Sigmatropic reaction simple english wikipedia, the free. Aryl allyl ethers undergo a thermal rearrangement to give orthoallylphenols. Illustrated glossary of organic chemistry 1, 3 hydrogen shift or 1, 3 h shift. The starting material is a benzyl allyl ether and undergoes 2,3sigmatropic rearrangement to make a new cc sigma bond at the expense of a co sigma bonda bad bargain this as the co bond is stronger.
A formal 3,3sigmatropic rearrangement route to quaternary. Among pdiicatalyst candidates examined, phosphinecoordinated complexes, such as cl 2 pdpph 3 2 or cl 2 pddppf gave little to no product. Provided that reactions were carried out in mecn, pdoac 2 and pdcl 2 catalysts gave the desired formal 3,3sigmatropic rearrangement. At the newly formed double bond there is a strong preference for formation of the ealkene or trans isomer product. The reaction of ketene silyl acetal derived from optically active 1phenylethyl 2methylpropanoate mainly proceeds with the retention of chirality at the benzyl position to give the corresponding optically active silyl ester under thermodynamic conditions. Apr 09, 2015 3, 3 sigmatropic rearrangement upei organic. The 3,3sigmatropic rearrangement of alkenyl 1naphthyl sulfides in solutions with various polarities was investigated at 8190 c.
A sigmatropic rearrangement in which a hydrogen atom migrates to a new spot two atoms away from its starting spot, with simultaneous shift of a pi bond. The formation of a carbonyl group makes this reaction, unlike other sigmatropic rearrangements, inherently irreversible. The vinylcyclobutanetocyclohexene rearrangement has been known for over 40 years. The 3, 3 sigmatropic rearrangement of 1, 5dienes or allyl vinyl. A large number of 2,3sigmatropic rearrangements have been studied. The cope rearrangement is an extensively studied organic reaction involving the 3,3 sigmatropic rearrangement of 1,5dienes. Pdf 2,3sigmatropic rearrangements of propargylic and.
Application to the stereoselective synthesis of f juvabione david a. Illustrated glossary of organic chemistry 1,3hydrogen shift. Within the context of projecting the steric course of the proposed sigmatropic rearrangement outlined in scheme 111, as applied. A sigmatropic reaction in organic chemistry is a pericyclic reaction wherein the net result is one.
A large number of 2, 3 sigmatropic rearrangements have been studied. The mechanism below is from the clayden group at manchester uni. For example, a 1,3 sigmatropic rearrangement describes a reaction in which the residue migrates from position 1 to position 3. In this chapter, the 1,2 and 2,3rearrangements of ylides, the 2,3wittig and the aza2,3wittig rearrangements, and the 3,3sigmatropic rearrangement are discussed, including some mechanistic aspects followed by some pertinent examples of their application in stereoselective synthesis. Asymmetric 2,3sigmatropic rearrangement of allylic. Illustrated glossary of organic chemistry 1,3hydrogen shift or 1,3h shift. The 3, 3 sigmatropic rearrangement of 1,5dienes or allyl vinyl ethers, known respectively as the cope and claisen rearrangements, are among the most commonly used sigmatropic reactions. The thermal 1,3 shift of a saturated carbon by mechanism a below is. Weeks department of chemistry, north carolina state university, p. The rates and equilibrium constants of the rearrangement were measured. There are two different types of sigmatropic reaction, a those that involve the migration of a hydrogen atom and b those that involve a carbon or other atom. The rearrangement is in a good agreement with the stability feature of saytzev olefin. For the pericyclic reactions website, follow this link.
H 2c c h chch 3 h w w h c w h h 2c chch 3 1 1 2 3 w w h c w h h 2c chch 3 1 1 2 3 a 1, 3 sigmatropic rearrangement. The wellknown claisen rearrangement is a concerted 3,3sigmatropic process. The most common category of hydrogen shift involves a so called 1,5 hydrogen sigmatropic shift n1 in the above diagram. The name sigmatropic is the result of a compounding of the longestablished sigma designation from single carboncarbon bonds and the greek word tropos, meaning turn. A video presentation of the 3, 3 sigmatropic rearrangement for chemistry 342 at upei. They were easily converted into diversely substituted 1,3. In reality, 1,3 carbon shifts may be more complex, a fair number of them proceeding via. Journal of fluorine chemistry, 56 1992 165173 3, 3 sigmatropic rearrangements of fluorinated compounds suzanne t. This descriptor unfortunately implies three sequential tandem events, or six. The cope rearrangement is an extensively studied organic reaction involving the 3,3sigmatropic rearrangement of 1,5dienes. It is perhaps surprising that these two rearrangements may sometimes be found in. Electrocyclic reaction or sigmatropic rearrangement. Therefore, the this c rehybridizes to sp 2, and the new p orbital becomes part of the new pi bond. In this chapter, the 1,2 and 2, 3 rearrangements of ylides, the 2, 3 wittig and the aza2, 3 wittig rearrangements, and the 3, 3 sigmatropic rearrangement are discussed, including some mechanistic aspects followed by some pertinent examples of their application in stereoselective synthesis.
The results suggest that the fact that the reaction rate will increase as the electron. For example 3methyl1,5hexadiene heated to 300c yields 1,5heptadiene. Mar 24, 2014 a video presentation of the 3, 3 sigmatropic rearrangement for chemistry 342 at upei. Applications of 2,3sigmatropic rearrangements to natural. Three examples of the cope rearrangement are shown in the following diagram. Request pdf a general photoinduced sequential electrocyclization 1,9sigmatropic rearrangement ring opening reaction of. The reaction is degenerate, meaning that the starting material is identical with the product. The following reactions are unified in that they combine claisen reaction with a. Pdf 3,3 sigmatropic rearrangement of 3alkynyladenines. Sigmatropic rearrangements the cope rearrangement sigmatropic rearrangements the claisen rearrangement is a sigmatropic rearrangements today chapter 18 benzene stability of benzene aromaticity other aromatic compounds nomenclature of substituted benzenes reactions at the benzylic. The driving force behind most 2, 3 sigmatropic rearrangements is the transformation of an unstable carbanion into a stable product. Stereochemical study of the 3,3 sigmatropic rearrangement of 1,5diene3alkoxides.
H 2c c h chch 3 h w w h c w h h 2c chch 3 1 1 2 3 w w h c w h h 2c chch 3 1 1 2 3 a 1,3 sigmatropic rearrangement. For example, 3methyl1,5hexadiene heated to 300 c yields 1,5heptadiene. The suprafacial 1, 3 sigmatropic rearrangement is an orbital symmetry forbidden process, and thus typically has high activation barriers and potentially proceeds through radical or zwitterionic intermediates. Reactions 1 and 2 top row demonstrate the stereospecificity. Journal of fluorine chemistry, 56 1992 165173 3,3sigmatropic rearrangements of fluorinated compounds suzanne t. Pericyclic reactions sigmatropic rearrangements introduction and 1, 3 migrations pericyclic reactions and organic photochemistry. Selenoxide elimination and 2,3sigmatropic rearrangement. This c rehybridizes to sp 3 as the h migrates and becomes sigma bonded to it.
For example, a 1, 3 sigmatropic rearrangement describes a reaction in which the residue migrates from position 1 to position 3. The most wellknown of the sigmatropic rearrangements are the 3,3 cope rearrangement, claisen rearrangement, carroll rearrangement, and the. Sigmatropic rearrangements in stereoselective synthesis. Enantiomerically pure c,dring allylic alcohol 4 stereospecifically undergoes five types of 3,4sigmatropic rearrangements to give c23 functionalized 16ene vitamin d 3 sidechain units with natural c. An example of claisen rearrangement is the 3,3 rearrangement of an allyl vinyl ether, which upon heating yields a.
Cycloaddition reactions occur when two or more reactants combine additively to form a cyclic. Pericyclic reactions sigmatropic rearrangements nptel. Elimination of sulfonyl radicals by everett ben hay b. The suprafacial 1,3sigmatropic rearrangement is an orbital symmetry forbidden process, and thus typically has high activation barriers and potentially proceeds through radical or. These rearrangements of 1,5diene systems, discovered first by hurd and later by cope, are generally called cope rearrangements. In 1,5cyclohexadiene, the parent system for 3,3 sigmatropic rearrangements, reaction takes place at 300c with an activation energy barrier of approximately 34 kcalmol.
Utilizing the reduction of ring strain helps to increase the thermodynamic driving force in 3, 3 sigmatropic rearrangements and to lower the activation energy. It is a 3,3 sigmatropic rearrangement with only carbon atoms involved in the six membered transition state why is it called 3,3. Analyzing such reactions in more detail, the chiralityinducing step is run prior to the cope rearrangement. A computational study provides evidence on the feasibility of the. Box 8204, raleigh, nc 276958204 usa received july 3, 1991. The nomenclature of 1,n sigmatropic rearrangements derives from the position of the residue r before and after the reaction. They can be divided into three types, depending on the nature of the charge relationships between the xy fragment. Request pdf a general photoinduced sequential electrocyclization 1,9sigmatropic rearrangement ringopening reaction of. The wellknown claisen rearrangement is a concerted 3, 3 sigmatropic process. Thus, the 3, 3 sigmatropic rearrangement is conducted under the wellknown 1, 3. Cope rearrangements the rearrangement of 1,5hexadiene is the simplest cope rearrangement. Among the fundamental chemical transformations in organic synthesis, the 3,3sigmatropic rearrangement occupies a unique position as a powerful, reliable, and welldefined method for the stereoselective construction of carboncarbon or carbonheteroatom bonds.
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