Furans and their Benzo Derivatives: (ii) Reactivity

Sargent, Melvyn V.; Dean, F. M.

doi:10.1016/b978-008096519-2.00061-8

Cited by 51 publications

(17 citation statements)

References 274 publications

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“…Among the solutions investigated to date to improve the reaction are catalysis using Lewis acids [1], metal salts and complexes [2], Cu 2 § [3 ], silica gel [3], zeolites [4,5], ultrasound [6], centrifugation [ 7], and high-pressure techniques [8]. Owing to the abundance of the instances of furan [4 + 2] cycloadditions in the literature, and the reviews that have already appeared [9,10], highlights of this reaction in the cases where extensive work has been published on the subsequent ring opening will be outlined.…”

Section: [4+ 2] Cycloodditions With Dienophilesmentioning

confidence: 99%

Using ring-opening reactions of oxabicyclic compounds as a strategy in organic synthesis

Chiu

Lautens

1997

Topics in Current Chemistry

149

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Section: [4+ 2] Cycloodditions With Dienophilesmentioning

confidence: 99%

Using ring-opening reactions of oxabicyclic compounds as a strategy in organic synthesis

Chiu

Lautens

1997

Topics in Current Chemistry

149

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“…The importance and versatility of the Diels−Alder reaction for the construction of unsaturated six-membered ring systems is well documented in the literature − By far the most extensively studied five-membered heteroaromatic system for Diels−Alder cycloaddition is furan and its substituted derivatives. − The resultant 7-oxabicyclo[2.2.1]heptanes are valuable synthetic intermediates which have been further elaborated to substituted arenes, carbohydrate derivatives, and various natural products. − A crucial synthetic transformation employing these intermediates involves cleavage of the oxygen bridge to produce functionalized cyclohexene derivatives. − In many cases, however, the Diels−Alder strategy is not feasible because of the low reactivity of furan toward monoactivated dienophiles. …”

mentioning

confidence: 99%

IMDAF Cycloaddition as a Method for the Preparation of Pyrrolophenanthridine Alkaloids

et al. 1998

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Acylation of 5-amino-2-furancarboxylic acid methyl ester with alkenoyl acid chlorides gives 2-amidofurans that undergo intramolecular Diels−Alder cycloadditions. The reactions occur at 165 °C in toluene or at 100 °C when 4 M ethereal LiClO4 was used as the solvent. The resultant dihydroindoles are formed by the nitrogen lone pair assisted ring opening of the initial oxa-bridged cycloadducts, followed by loss of water. Under certain conditions, alternative cationic cyclization routes become important pathways. Several members of the pyrrolophenanthridine class of alkaloids were obtained by a short, efficient method based on the intramolecular Diels−Alder furan cycloaddition of 2-amidofurans containing a tethered alkenyl group. The resulting dihydroindoles were elaborated in one step to the 1H-pyrrolo[3,2,1-de]phenanthridine ring system by a free radical induced cyclization using bis(tributyltin).

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“…Heterocycles such as furan, thiophene, and pyrrole undergo Diels−Alder reactions despite their stabilized 6π-aromatic electronic configuration. − By far the most extensively studied five-ring heteroaromatic system for Diels−Alder cycloaddition is furan and its substituted derivatives. , The resultant 7-oxabicyclo[2.2.1]heptanes are valuable synthetic intermediates that have been further elaborated to substituted arenes, carbohydrate derivatives, and various natural products. − A crucial synthetic transformation employing these intermediates involves the cleavage of the oxygen bridge to produce functionalized cyclohexene derivatives. − In many cases, however, this strategy is not feasible because of the low reactivity of furan toward monoactivated dienophiles. , Lewis acid catalysis, interaction with metals, or use of high pressure helps to overcome the sluggishness of furan toward Diels−Alder cycloaddition. Incorporation of an electron-donating group onto the 2-position of furan has also been employed as a means to enhance the reactivity of the heteroaromatic ring system .…”

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confidence: 99%

Diels−Alder Reaction of 2-Amino-Substituted Furans as a Method for Preparing Substituted Anilines

et al. 1997

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5-Amino-2-furancarboxylic acid methyl ester undergoes a facile Diels−Alder cycloaddition with a variety of dienophiles to afford ring-opened cycloadducts that are readily dehydrated using BF3· OEt2 to give polysubstituted anilines. In each case, the cycloaddition proceeds with high regioselectivity, with the electron-withdrawing group being located ortho to the amino group. The most favorable FMO interaction is between the HOMO of the furanamine and the LUMO of the dienophile. The atomic coefficient at the ester carbon of the furan is larger than that at the amino center, and this nicely accommodates the observed regioselectivity. The [4 + 2]-cycloaddition of N-(5-nitrofuranyl)morpholine with methyl vinyl ketone affords a mixture of three phenols. One of the phenols is derived from a Diels−Alder reaction followed by nitro group ejection and subsequent aromatization. The remaining two phenols are the result of cleavage of the initially formed oxabicyclic intermediate with concomitant migration of the nitro group. The mild reaction conditions with which furan-2-carbamic acid tert-butyl ester undergoes Diels−Alder cycloaddition with N-phenylmaleimide allow for the ready isolation of the initial oxybridged cycloadduct.

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Furans and their Benzo Derivatives: (ii) Reactivity

Cited by 51 publications

References 274 publications

Using ring-opening reactions of oxabicyclic compounds as a strategy in organic synthesis

Using ring-opening reactions of oxabicyclic compounds as a strategy in organic synthesis

IMDAF Cycloaddition as a Method for the Preparation of Pyrrolophenanthridine Alkaloids

Diels−Alder Reaction of 2-Amino-Substituted Furans as a Method for Preparing Substituted Anilines

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