Cycloaddition reaction of methyl 2-pyronecarboxylates with 1,3-dienes

Imagawa, Takeshi; Haneda, Akira; Nakagawa, T.; Kawanisi, Mituyosi

doi:10.1016/0040-4020(78)80094-5

Cited by 10 publications

(2 citation statements)

References 21 publications

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“…Regioselective use of an unactivated pyrone as a two-carbon unit in what is formally a [4 + 2] cycloaddition is scarce, with only the 5-substituted pyrone enabling regioselectivity, but not chemoselectivity . Other substitution formats resulted in a blend of diene and dienophile roles for the pyrone and a lack of regioselectivity, particularly with 6-substituted pyrones . These findings made it unclear what conditions would enable the successful use of 6-substituted pyrones as dienophiles (their use as dienes is known) , and what substitution pattern would result in the absence of a directing Staunton–Weinreb-type leaving group.…”

Section: Introductionmentioning

confidence: 99%

“… 16 Other substitution formats resulted in a blend of diene and dienophile roles for the pyrone and a lack of regioselectivity, particularly with 6-substituted pyrones. 17 These findings made it unclear what conditions would enable the successful use of 6-substituted pyrones as dienophiles (their use as dienes is known) 18 , 19 and what substitution pattern would result in the absence of a directing Staunton–Weinreb-type leaving group. Thus, we investigate the parameters that would enable the regioselective use of pyrones as dienophiles toward the synthesis of thermorubin.…”

Section: Introductionmentioning

confidence: 99%

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Regioselective Annulation of 6-Carboxy-Substituted Pyrones as a Two-Carbon Unit in Formal [4 + 2] Cycloaddition Reactions

Kohanov,

Shuvo,

Lowell

2024

J. Org. Chem.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Regioselective Annulation of 6-Carboxy-Substituted Pyrones as a Two-Carbon Unit in Formal [4 + 2] Cycloaddition Reactions

Kohanov,

Shuvo,

Lowell

2024

J. Org. Chem.

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The IntramolecularDiels–Alder Reaction

Ciganek

1984

Organic Reactions

108

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The Diels–Alder reaction is one of the most useful reactions available to the synthetic organic chemist. It is thus surprising that the intramolecular version, in which both diene and dienophile are part of the same molecule, remained virtually unexplored for many years. Early examples were often the result of unexpected observations, and the many advantages of this reaction were recognized and put to use in the synthesis of complex polycyclic molecules only recently. In the intramolecular Diels–Alder reaction, two rings are formed in one step. In addition to the six‐membered ring formed by the [4 + 2]cycloaddition, the product contains a second ring, the size of which depends on the length of the chain connecting diene and dienophile. Of the two possible regiochemical modes of addition, that leading to the fused product usually predominates to the virtual exclusion of the bridged product. The Diels–Alder reaction proceeds through a highly ordered transition state that is reflected in large negative activation entropies. In the intramolecular version, some of the ordering has been accomplished in advance by making the two reacting functionalities part of the same molecule. This results in less negative activation entropies and increased reaction rates under often surprisingly mild conditions. On the other hand, by using forcing conditions one can sometimes carry out intramolecular Diels–Alder additions that would be doomed to failure in the intermolecular version. Lower reaction temperatures, together with the constraints imposed by the connecting chain, often result in pronounced regio‐ and stereoselectivity. Side reactions such as dimerization or polymerization can be avoided by using high dilution or low pressures in the gas phase. Examples where the bimolecular Diels–Alder reaction interferes with the intramolecular cyclization are rare. All of these features suggest that the intramolecular Diels–Alder reaction should be considered for any synthesis of a molecule containing a six‐membered ring fused to a second ring, especially if that ring is five‐ or six‐membered. Such a synthetic scheme may be made convergent by building up the diene and dienophile portions separately and connecting them just prior to the actual cyclization. Another potential use of the intramolecular Diels–Alder reaction that has not received much attention to date is as a supplement to the intermolecular Diels–Alder reaction in cases where the latter is unsuccessful or gives the wrong regio‐ or stereochemistry. By judicious choice of the connecting chain, the reaction may be made to proceed with the desired selectivity; this is followed by cleavage of the chain and conversion of the two ends to the desired functionalities. Once the feasibility of employing the intramolecular Diels–Alder reaction has been recognized, the main challenge often becomes the preparation of the substrate. A discussion of that aspect is beyond the scope of this chapter; however, by scanning the tables for the particular diene, dienophile, and chain one is interested in, and then referring to the original literature, it will often be possible to obtain some indications on how to proceed. An attempt has been made to cover the literature of the thermal intramolecular Diels–Alder reaction as completely as possible up to and including the year 1981. Many of the papers that appeared in 1982 and some from 1983 have also been included. More recent references are given in an addendum at the end of the tabular survey.

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The Retro–Diels–Alder Reaction PartII. Dienophiles with One or More Heteroatom

Rickborn

1998

Organic Reactions

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This review (Part II) is topically organized around the dienophile that is generated in a retro [4 + 2] reaction, and to the extent possible follows the principles adopted for Part I, which covers reactions in which both dienophile bonding centers are carbon atoms. The present chapter encompasses retro–Diels–Alder (rDA) reactions in which one or both of the dienophile reaction centers are heteroatoms. Any of the other atoms in the starting material (cycloadduct) may be carbon or heteroatom. Substituents on all positions are encompassed, and any bond order available to any oxidation state of an element is included, as is bonding to non‐nearest neighbor atoms (e.g., bicyclics). The reader is directed to Part I (Vol. 52) for general discussion of the rDA reaction, the features that affect rates and outcome, and the use of acids, bases, other catalysts, and scavengers. Certain subclassifications (e.g., processes proposed under MS conditions, polymer applications) of rDA reactions have been omitted from both sections; these topics are listed in the Introduction to Part I. Citations to over 100 reviews on various aspects of the rDA reaction are collected at the beginning of the References to Part I. Those that are especially pertinent to Part II will be repeated here, in the context of the particular dienophile under discussion. The decision to split the review of the rDA reaction into two parts was based on the volume of literature encountered, as outlined in the Introduction to Part I. Active literature searching was concluded for both Parts in April 1995, although occasional more recent references have been included.

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Cycloaddition reaction of methyl 2-pyronecarboxylates with 1,3-dienes

Cited by 10 publications

References 21 publications

Regioselective Annulation of 6-Carboxy-Substituted Pyrones as a Two-Carbon Unit in Formal [4 + 2] Cycloaddition Reactions

Regioselective Annulation of 6-Carboxy-Substituted Pyrones as a Two-Carbon Unit in Formal [4 + 2] Cycloaddition Reactions

The IntramolecularDiels–Alder Reaction

The Retro–Diels–Alder Reaction PartII. Dienophiles with One or More Heteroatom

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