2.03 Prins Reactions and Carbonyl, Imine, and Thiocarbonyl Ene Reactions

Snider, Barry B.

doi:10.1016/b978-0-08-097742-3.00203-2

Cited by 23 publications

(12 citation statements)

References 391 publications

(233 reference statements)

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“…Inspired by the B–N reaction, we opted for the in situ activation of the amide group. Considering the low efficiency of the classical amide activators such as P 2 O 5 and POCl 3 3 4 10 , highly electrophilic trifluoromethanesulfonic (triflic) anhydride (Tf 2 O) 28 was selected for our purpose. Tf 2 O in combination with a base such as 2,6-di- tert -butyl-4-methylpyridine (DTBMP) 29 , Hünig base 30 , 2-chloropyridine 31 , 2-fluoropyridine 32 33 34 35 36 , 2-iodopyridine 37 , 2,4,6-collidine 38 39 40 41 , and 3-cyanopyridine 42 had been employed for the activation of amides in various C–C bond-forming reactions.…”

Section: Resultsmentioning

confidence: 99%

“…The direct reaction of a weak nucleophile with a weak electrophile (Nu w -El w ) is difficult under conventional reaction conditions. Alkenes are a class of stable and easily available weak π-nucleophiles, which can only undergo transition metal-mediated C–C bond forming reactions, or react with reactive electrophiles such as acyl chlorides (Friedel-Crafts acylation of alkenes) 2 or in situ generated highly electrophilic intermediates, such as nitrilium ions [the extended Bischler–Napieralski (B–N) reaction 3 4 5 6 7 ], iminium 8 / N -acyliminium ions 9 , and acid-activated aldehydes/ketones (Prins reaction 10 ). On the other hand, although nitrilium ions are key intermediates in several classical reactions such as Houben-Hoesch 11 , Ritter 12 13 , von Braun 13 , Bischler-Napieralski 13 , Beckmann 13 , Schmidt 13 , and Ugi reactions 14 , their participation in synthetically useful intermolecular reactions with alkenes is unknown.…”

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confidence: 99%

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Metal-Free C–H Alkyliminylation and Acylation of Alkenes with Secondary Amides

Huang

Geng

et al. 2016

Sci Rep

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Carbon–carbon bond formation by metal-free cross-coupling of two reactants with low reactivity represents a challenge in organic synthesis. Secondary amides and alkenes are two classes of bench-stable compounds. The low electrophilicity of the former and low nucleophilicity of the latter make the direct coupling of these two partners challenging yet highly desirable. We report herein an unprecedented intermolecular reaction of secondary amides with alkenes to afford α,β-unsaturated ketimines or enones, which are versatile intermediates for organic synthesis and are prevalent in bioactive compounds and functional materials. Our strategy relies on the chemoselective activation of the secondary amide with trifluoromethanesulfonic anhydride (Tf2O)/2-fluoropyridine to generate a highly reactive nitrilium intermediate, which reacts efficiently with alkenes. This metal-free synthesis is characterized by its mild reaction conditions, excellent functional group tolerance and chemoselectivity, allowing the preparation of multi-functionalized compounds without using protecting groups.

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Metal-Free C–H Alkyliminylation and Acylation of Alkenes with Secondary Amides

Huang

Geng

et al. 2016

Sci Rep

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“…As evidenced by its extensive utility in the synthesis of a number of bioactive targets, the alkynyl oxa-Prins and aza-Prins reactions serve as powerful and versatile methods for the preparation of complex dihydrofurans, -pyrans, -pyrrolidines, and -piperidines (Scheme a) . The acid-catalyzed condensation of alkynyl alcohols/amines with aldehydes or ketones, followed by the intramolecular cyclization of the alkyne onto an oxocarbenium/iminium intermediate and terminal nucleophilic capture, furnishes oxa- and azacycles.…”

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confidence: 99%

One-Pot Double-Annulation Strategy for the Synthesis of Unusual Fused Bis-Heterocycles

et al. 2020

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A novel metal-free double-annulation cascade for the construction of unusual fused heterocyclic systems is described. This simple protocol enables the sequential assembly of two rings in one pot from two simple precursors. Acidic conditions promote the condensation and the intramolecular alkynyl Prins reaction of an enyne or arenyne alcohol with a cyclic hemiaminal to form a five-, six-, or seven-membered oxacycle followed by a seven- or eight-membered azacycle. In this transformation, chemical complexity is rapidly generated with the formation of three new bonds (one C–O, one C–C, and one C–N) in one synthetic operation. The strategy is modular and relatively general, providing access to a series of unique fused bicyclic scaffolds.

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“…Alternatively, another large collection of transformations converts their related C–H bonds, either at allylic or vinylic positions, into functional groups while retaining or restoring the π components (Scheme , B). Exemplified by ene and Prins reactions, Heck reaction, and recently developed catalytic allylic and vinylic C–H bond functionalization reactions, these processes are particularly useful as they produce functionalized alkenes with the retained degree of unsaturation, which still allow for further alkene transformations.…”

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confidence: 99%

Fe(III)-Based Tandem Catalysis for Amidomethylative Multiple Substitution Reactions of α-Substituted Styrene Derivatives

et al. 2020

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Developing tandem multiple C–H substitution reactions of simple alkenes provides rapid access to structurally complex unsaturated building blocks. Amidomethylative reactions that reserve CC double bonds have been composed sequentially for tandem catalytic substitutions around the CC bonds of alkenes. As a proof-of-concept demonstration, tandem catalytic amidomethylative processes, which effectively form multiple C–C bonds, have been developed to directly and selectively transform α-substituted styrenes into unsaturated N-heterocycles. Using Fe(OTf)3 as the sole catalyst, the operationally simple protocols employ bench-stable bisamidomethane as the sole reagent to produce hexahydropyrimidines and 1,2,3,6-tetrahydropyridine derivatives. Moreover, the practical catalytic processes constituted facile two-step pathways, from simple α-substituted styrenes, to access unsaturated 1,3-diamine and bispidine derivatives.

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2.03 Prins Reactions and Carbonyl, Imine, and Thiocarbonyl Ene Reactions

Cited by 23 publications

References 391 publications

Metal-Free C–H Alkyliminylation and Acylation of Alkenes with Secondary Amides

Metal-Free C–H Alkyliminylation and Acylation of Alkenes with Secondary Amides

One-Pot Double-Annulation Strategy for the Synthesis of Unusual Fused Bis-Heterocycles

Fe(III)-Based Tandem Catalysis for Amidomethylative Multiple Substitution Reactions of α-Substituted Styrene Derivatives

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