Cycloaddition of 2<i>H</i>‐Pyran‐2‐thiones with Nitroso Derivatives. An Unexpected Cycloaddition‐Rearrangement Reaction

Defoin, Albert; Augelmann, Gérard; Fritz, Hans; Geffroy, Guillaume; Schmidlin, C.; Streith, Jacques

doi:10.1002/hlca.19850680724

Cited by 23 publications

(5 citation statements)

References 40 publications

(18 reference statements)

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“…Synthesis of Sulfur Analogues of α - Pyrone. 2 H -Pyran-2-thione was obtained from α−pyrone and 2,4-bis(4-methoxyphenyl)-2,4-dithioxo-1,3,2,4-dithiadiphosphetane (Lawesson's Reagent) as described by Defoin et al The 2 H -thiopyran-2-one was produced from 2 H -pyran-2-thione by pyrolysis, as described in reference 15.…”

Section: Methodsmentioning

confidence: 99%

Photochemical Ring-Opening and Intramolecular Hydrogen Shift Reactions in Sulfur Analogues of α-Pyrone

et al. 2006

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A combined matrix isolation FTIR and theoretical DFT(B3LYP)/6-311++G(d,p) study of the photochemistry of sulfur analogues of alpha-pyrone [2H-thiopyran-2-one (TP) and 2H-pyran-2-thione (PT)] was carried out. The vibrational spectra of monomers of the compounds isolated in low-temperature argon matrixes were studied experimentally and assigned completely on the basis of theoretical calculations. UV irradiation (lambda > 337 nm) of the studied compounds isolated in low-temperature matrixes results mainly in the ring-opening reaction by means of the cleavage of the alpha-bond. Other photoprocesses, not involving the alpha-bond-cleavage step (such as generation of Dewar valence isomer), correspond to the minor reaction channels in both studied compounds. The ring-opening photoreaction in PT represents the first reported case of an alpha-bond cleavage in a compound with a C=S group attached to a six-membered ring, in which the internal strain practically does not exist, whereas the corresponding reaction in TP (a cleavage of a C-S bond in the alpha position with respect to a carbonyl group) is now reported for the first time. Following the ring-opening reactions, isomerization processes and intramolecular hydrogen shift reactions were observed, enabling production of TP from PT and vice versa. A detailed study of such processes was undertaken, and kinetical and mechanistical data are presented and discussed.

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Section: Methodsmentioning

confidence: 99%

Photochemical Ring-Opening and Intramolecular Hydrogen Shift Reactions in Sulfur Analogues of α-Pyrone

et al. 2006

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“…Among the proposed hypothetical mechanisms, the most plausible ones were published in 1988 [27]. In this contest, one of the proposed mechanisms came very close to the one we had described in 1985 (see Scheme 2 ) [26], compound 19 also being the key intermediate. Furthermore, this reaction sequence was used as a testing ground for some new software packages ~ for example Ugi's RAIN and PEMCD programs [27] [28], which have been developed to unravel complex reaction mechanisms.…”

Section: C(6)mentioning

confidence: 67%

“…Overall, these various non-stop cascading processes represent strongly exothermal reactions, as demonstrated, for example, in the above described reaction [26]. This is to say that an energy cascade is operating along the reaction sequence, the final reaction products being particularly stable.…”

Section: C(6)mentioning

confidence: 92%

“…In [25], we described the reaction of 2H-pyran-2-thione (16) and of some of its derivatives with nitroso-dienophiles which gave the 'adducts' 22 in good-to-excellent yields. Formation of these latter products led us to postulate and then to demonstrate, the essential features of the mechanism of this cascade reaction which consists of no less than six consecutive reaction steps (Scheme 5 ) [26]: i ) a rate-determining regiospecific DielsAlder cycloaddition leading to 17; ii) formation of betaine 18 by a push-pull ring-opening mechanism; iii) ring-closure of 18 by an intramolecular nucleophilic 1,4-addition leading to the key intermediate 19, which was isolated and characterised in a few cases, e.g. when R = C0,Bn; iv) a retro-Diels-Alder reaction which is due both to the specific positioning of the double bond and to the weak N-0 bond; u ) a [1,5]-sigmatropic acyl migration from the S-to the N-atom, and vi) an intramolecular hetero-Diels-Alder cy~loaddition~).…”

Section: C(6)mentioning

confidence: 98%

“…This cascade-reaction sequence seems to be of relatively broad scope [26]. For the sake of clarity, various substitution patterns have been omitted and replaced by a didactic labelling (dots and squares) in Scheme 5 .…”

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Cascade Reactions. A Simple One‐pot Synthesis of the Mitomycin Skeleton

Defoin

Geffroy

Nouën

et al. 1989

Helvetica Chimica Acta

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~ ~Nitroso-arene dienophiles 1 react regiospecifically with the conjugated dienals 2 and 3a/3b, and lead thereby to the unstable Dzels-Alder cycloadducts 4 and 5 These undergo two types of cascade reactions which give pyridmium betaines 6 and pyrrolo-indoles 8 as the major reaction products The one-pot syntheses of pyrroloindoles 8 represent a new and easy access to the basic skeleton of mitomycins 10 The scope and limitations of the cascade reactions were investigated Diels-Alder Cycloadditions of Nitroso-arene Dienophiles with Conjugated Dienals and their Cascade Reactions'). -We shall describe herein some cascade-reaction sequences which we observed, when conjugated dienals were treated with nitrosoarene dienophiles 1. To our knowledge, no cycloaddition reactions have been described so far between nitroso dienophiles and linear conjugated dienals. Nevertheless, some oximeand dimethylacetal derivatives of these dienals are known to undergo Diels-Alder reactions with nitroso dienophiles [2-71.The reaction of nitrosobenzene with pentadienal2 or with the commercially available mixture of hexadienals 3a (80 YO) and 3b (20 YO) occurred rapidly leading, in each instance, to four heterocyclic products, none of which being the expected primary Diels-Alder adduct. For example, the reaction of pentadienal 2 with PhNO gave the betaine 6a, trace amounts of the pyrrole-2-carbaldehyde 7a, the tricyclic alcohol 8a, and the corresponding ketone 9a (Scheme I). It should be noted that the preparation of the tricyclic products 8a and 9a, via a different multistep approach, had already been described as part of a synthetic plan for the mitomycins [8-lo].Mitomycins 10 represent a class of well-known natural products [l 11 which exhibit antibiotic and antitumor properties [12].Since our procedure for the synthesis of pyrrolo-indoles 8a/8b and 9a/9b represents a new one-pot process, using easily available starting materials, we decided to investigate the scope and limitations as well as the mechanism of these obviously complex cascade reactions (see below), our ultimate goal being the synthesis of some mitomycin derivatives.

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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 of 2H‐Pyran‐2‐thiones with Nitroso Derivatives. An Unexpected Cycloaddition‐Rearrangement Reaction

Cited by 23 publications

References 40 publications

Photochemical Ring-Opening and Intramolecular Hydrogen Shift Reactions in Sulfur Analogues of α-Pyrone

Photochemical Ring-Opening and Intramolecular Hydrogen Shift Reactions in Sulfur Analogues of α-Pyrone

Cascade Reactions. A Simple One‐pot Synthesis of the Mitomycin Skeleton

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

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