Halogenated ketenes. IX. Ketene carbodiimide cycloadditions

Brady, William T.; Dorsey, Edwin D.; Parry, Fred H.

doi:10.1021/jo01262a011

Cited by 41 publications

(8 citation statements)

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“…[11b] 5-chloro-2-azidobenzylamine (3 c), [11c] ethyl phenyl ketene [31] and methyl phenyl ketene [32] were prepared following previously reported procedures. N-(2-Azidobenzyl)imines (4) and N-(2-azidophenethyl)imines were obtained by standard procedures (Scheme 1, Methods A, B and C).…”

Section: Methodsmentioning

confidence: 99%

“…) and 31 P NMR spectroscopy, was completed in less than 1 h. [14] The isolation and purification of 5 were prevented by the extreme hydrolytic sensitivity of the phosphazene group. When these compounds were treated in the same reaction flask with methyl phenyl ketene or ethyl phenyl ketene at room temperature, the pale yellow reaction mixture immediately turned orange and then slowly faded to a colourless solution.…”

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confidence: 99%

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Surpassing Torquoelectronic Effects in Conrotatory Ring Closures: Origins of Stereocontrol in Intramolecular Ketenimine-Imine [2+2] Cycloadditions

et al. 1999

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Intramolecular ketenimine ± imine [22] cycloadditions leading to 1,2-dihydroazeto[2,1-b]quinazolines occur in a notably stereocontrolled manner along the newly formed C ± C single bond when prochiral ketenimine and imine fragments are combined. Computational studies support stepwise mechanisms for these reactions. In sharp contrast with other well-known [22] cycloadditions, the first step of the reaction determines its stereochemical outcome, thereby surpassing the low stereocontrol induced by torquoelectronic effects.

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Surpassing Torquoelectronic Effects in Conrotatory Ring Closures: Origins of Stereocontrol in Intramolecular Ketenimine-Imine [2+2] Cycloadditions

et al. 1999

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“…Eine Konsequenz dieser Betrachtungsweise ist, dass ungleich substituierte Ketene (13) in zwei ifbergangszustande (14 und 16) eintreten konnen, welche zu stereoisomeren Produkten (15 und 17) fuhren, da sich (aus Polarisationsgrunden, siehe oben) C1 des Cyclopentadiens immer rnit dem Carbonylkohlenstoff und C2 rnit Ccr des Ketens verbindet (punktierte Linien). Besteht nun ein wesentlicher Unter- 14 15 16 17 schied in der Raumbeanspruchung der zwei Ketensubstituenten (G = grosserer (sperrigerer) und K = kleinerer Substituent), dann durfte die Anordnung 14 spannungsmassig bevorteilt sein und der sperrigere Substituent (G) in entsprechendem Ausmasse mehr in die endo-Stellung (siehe 18) des Produktes 15 zu liegen kommen.…”

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Stereochemische Aspekte der Addition von Ketenen an Cyclopentadien

Rey

Roberts

Dieffenbacher

et al. 1970

Helvetica Chimica Acta

108

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Earlier work has shown that the cyclo-addition of a ketene to a conjugated diene is always (a) 2 + 2, (b) polarily directed, and (c) suprafacial with respect to the diene C=C. The adducts of ketenes and cyclopentadiene are thus always 7-substituted bicyclo [3.2.0] hept-2-ene-6-ones. New evidence is presented to show that unsymmetrically substituted ketenes add to cyclopentadiene in such a manner that the larger substituent has a greater tendency to take up the endoposition in the adduct. This is interpreted to mean that a ketene participates in such reactions antarafacially. Thus the ketene approaches cyclopentadiene (a) with its functional plane perpendicular to that of the ring, (b) with the carbonyl carbon over the middle of the ring, and (c) with the larger of the two substituents oriented preferentially away from the ring (transition state 11).This endo-specificity for the larger ketene substituent is demonstrated by the indicated endo/ exo ratios observed in the cyclo-adducts from ketenes with the following substituent pairs :C,H,/CH, = >95/<5, CH,/Cl = SO/ZO, CH,/CH=CH, = -65/35, C,H,/CH, = -60/40, n-C,H,/CH, = -60/40, CH,/Br = 56/44. These ratios enable a list to be compiled indicating the endo-specificity of the ketene substituents. The order closely parallels the space filling capacity as derived by other methods. The establishment of such ratios required reliable configurational assignments at carbon 7. These were derived by five methods based upon the following effects: (1) Both H-C7 and CH3-C7 cause nmr. signals at higher field in endo-position (compared with e m ) . (2) The CH,-C7 group in exo-position gives rise to a nuclear Overhauser effect with the vicinal H-C1, and in one case also with the trans-annular H-C5. (3) The nmr.-coupling constants of H-C7-exo (observed at H-C7) with H-C1 is always iarger than of H-C7-endo. (4) The coupling constant of H-C7-exo with H-C6(known to be exo-) of the LiAlH, reduction products of the cyclo-adducts (observed at H-C6) is always larger than that of H-C7-endo. (5) The nmr. signals of most protons in the cyclo-adducts are a t higher field in benzene than in chloroform solution; this "benzene shift" is larger for H-C7 or for CH,-C7 when in exo-than when in endo-position.Ketene (1) reagieren mit Olefinen (2) gewohnlich unter Bildung von Cyclobutanonen (3) [l] [a]. Die kinetischen Parameter und Losungsmitteleffekte zeigen [3], dass es sich -I -A-)=c=o .+ )={ + 4-4 1 2 3 dabei um eine Mehrzentren-Cycloaddition handelt . Zur Erklarung der Beschleunigung und der sehr wirksamen konstitutione118n Spezifitat bei Olefinen mit Donator-Substituenten (4) nimmt man einen polaren ubergangszustand (5) an [3]. Sorgfaltige x 1 4 5 Analysen der Cycloaddukte weisen auf eine ebenfalls sehr wirksame Stereospezifitat im Sinne einer syn-(= suprafacialen) Addition an das Olefin (6) [4] [5] hin. Besonders ---_ _---: f 6 interessant, und bis vor kurzem immer wieder zu Widerspruchen Anlass gebend, ist die offenbar stark bevorzugte ( 2 + 2)-Cycloaddition (7) auch in Fallen (8) wo eine (2 + ...

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“…The bromination of 7-exo-chloro-7-endo-phcnyl-bicyclo[3.Z.O]li~pt-2-en-6-one (12) [7] with 1 mol-equiv. of N-bromosuccinimide required 10 hours and addition of ben-…”

Section: )mentioning

confidence: 99%

“…endo-phenyl-~icyclo[3.Z.O]hept-2-en-7-one (14). A mixture of 6.55 g (30 mmol) of 7-exo-chloro-7-endo-phenyl-bicyclo[3.2.O]hept-2-en-6-one (12) [7], 5.5 g (31 mmol) of N-bromosuccinimide and a catalytic amount of benzoyl peroxide in 90 ml of carbon tetrachloride was heated over a light bulb for 10 h. Having removed the succinimide the solvent was evaporated yielding a brown oil which according to NMR. consisted of a 77:23 mixture of the ketones 13 and 14.…”

Section: -Exo-bromo-7-endo-t-butyl-bicyclo[32o]hept-z-en-6-onementioning

confidence: 99%

Synthesis and Properties of 3,7‐Dehydrotropones

Szechner

Dreiding

1976

Helvetica Chimica Acta

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Synthese und Eigenschaften von 3,7-Dehydrotroponen. -Zusammenfassung. 7-exoBrom-7-endo-t-butyl-(9) und 7-exo-Chlor-7-endo-phenyl-bicyclo[3.2.0] hept-Z-en-6-0n(l2) sowie 7,7- Aus der Behandlung der vier bromierten Bicycloheptenon-Derivate 10, 11 und 13 sowie 17 mit 1,l mol Triathylamin bei tiefer Temperatur liessen sich 2-t-Butyl-(5), 6-Brom-2-t-butyl-(6) und 2-Phenyl-3,7-dehydrotropon(7) sowie 2-Chlor-4,5-benzo-3,7-dehydro-tropon (8) isolieren.Das Reaktionsverhalten und die spektralen Eigenschaften (1H-NMR., 13C-NMR., IR. und UV.) der Dehydrotropone 5, 6, 7 und 8, sowie ihr Zusammenhang mit deren Struktur werden detailliert beschrieben.

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Halogenated ketenes. IX. Ketene carbodiimide cycloadditions

Cited by 41 publications

References 2 publications

Surpassing Torquoelectronic Effects in Conrotatory Ring Closures: Origins of Stereocontrol in Intramolecular Ketenimine-Imine [2+2] Cycloadditions

Surpassing Torquoelectronic Effects in Conrotatory Ring Closures: Origins of Stereocontrol in Intramolecular Ketenimine-Imine [2+2] Cycloadditions

Stereochemische Aspekte der Addition von Ketenen an Cyclopentadien

Synthesis and Properties of 3,7‐Dehydrotropones

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