scholarly journals Previtamin D: Z–E photoisomerization via a Hula-twist conical intersection

2019 ◽  
Vol 21 (13) ◽  
pp. 6776-6789 ◽  
Author(s):  
Werner Fuß
Keyword(s):  
Double Bond ◽  
Ring Opening ◽  
Main Product ◽  
Conical Intersection ◽  
Single Conformer

Ring opening of 7-dehydrocholesterol in a cold matrix yields a single conformer of previtamin D, a steroid Z-triene. On its photoisomerization, the main product results from Hula twist (HT), and side products (e.g. from double-bond twist, DBT) come from the same conical intersection.

scholarly journals Enhancement of strong-field multiple ionization in the vicinity of the conical intersection in 1,3-cyclohexadiene ring opening

2013 ◽  
Vol 139 (18) ◽  
pp. 184309 ◽  
Author(s):  
Vladimir S. Petrovic ◽  
Sebastian Schorb ◽  
Jaehee Kim ◽  
James White ◽  
James P. Cryan ◽  
...  
Keyword(s):  
Ring Opening ◽  
Strong Field ◽  
Conical Intersection ◽  
Multiple Ionization

Reactions of 4-Pyrones with Azomethine Ylides as a Chemo­selective Method for the Construction of Multisubstituted Pyrano[2,3-c]pyrrolidines

Synthesis ◽  
2021 ◽  
Author(s):  
Dmitrii L. Obydennov ◽  
Vyacheslav D. Steben’kov ◽  
Konstantin L. Obydennov ◽  
Sergey A. Usachev ◽  
Vladimir S. Moshkin ◽  
...  
Keyword(s):  
Double Bond ◽  
Ring Opening ◽  
Azomethine Ylides ◽  
Azomethine Ylide ◽  
Dipolar Cycloaddition ◽  
Computational Studies ◽  
Carbon Double Bond ◽  
Reactivity Indexes ◽  
Reaction Proceeds

Abstract4-Pyrones bearing electron-donating and electron-withdrawing groups react with nonstabilized azomethine ylides to form pyrano[2,3-c]pyrrolidines in moderate to good yields. The reaction proceeds chemoselectively as a 1,3-dipolar cycloaddition of the azomethine ylide at the carbon–carbon double bond of the pyrone activated by the electron-withdrawing substituent. The reactivity of 4-pyrones toward azomethine ylides was rationalized by computational studies with the use of reactivity indexes. The pyrano[2,3-c]pyrrolidine moiety could be modified, for example by a ring-opening transformation under the action of hydrazine to provide pyrazolyl-substituted pyrrolidines.

Reaktionen koordinierter Liganden, III [1]. Stabilisierung von Dimenthyldiphosphen und Menthylphosphiniden als Brückenliganden in Metallcarbonylkomplexen / Reaction of Coordinated Ligands, III [1]. Stabilization of Dim enthyldiphosphene and Menthylphosphinidene as Bridging Ligands in Metal Carbonyl Complexes

1986 ◽  
Vol 41 (5) ◽  
pp. 629-639 ◽  
Author(s):  
Anna-Margarete Hinke ◽  
Axel Hinke ◽  
Wilhelm Kuchen ◽  
Wolfgang Hönle
Keyword(s):  
Crystal Structure ◽  
Double Bond ◽  
Complex Formation ◽  
Main Product ◽  
Metal Carbonyl ◽  
Crystal Structure Analysis ◽  
Carbonyl Complexes ◽  
Bridging Ligands ◽  
Metal Carbonyl Complexes ◽  
Chromium Compounds

Abstract Reduction of MentPBr2M(CO)5 1 (M = Cr, W) with magnesium in THF yields the diphos­phene complex (CO)5M(Ment)P=P(Ment)M(CO)5 2 as the main product. In addition, a phosphinidene complex, (CO)5M(Ment)PM(CO)5 (3) is also formed. The latter is obtained in larger amounts, if the reaction is carried out in the presence of M(CO)5THF. The proposed structures are confirmed by NMR and UV data as well as - in the case of the chromium compounds (2a, 3a) - by crystal structure analysis. Compound 2a is obtained only as the frans-isomer. The P-P distance in 2a (204.0 pm) indicates a double bond which does not participate in the complex formation. The P-Cr distance in 3a (average: 230.3 pm) is within the low est range found for this element combination. Reaction of 2a with LiAlH4 yields the diphosphane complex (CO)5CrMent(H)P-P(H)MentCr(CO)5 4 as a mixture of “meso” and “rac” diastereomers.

Conical Intersection Mechanism for Photochemical Ring Opening in Benzospiropyran Compounds

1997 ◽  
Vol 119 (44) ◽  
pp. 10815-10820 ◽  
Author(s):  
Paolo Celani ◽  
Fernando Bernardi ◽  
Massimo Olivucci ◽  
Michael A. Robb
Keyword(s):  
Ring Opening ◽  
Conical Intersection

A P–H functionalized Al/P-based frustrated Lewis pair – hydrophosphination of nitriles, ring opening with cyclopropenones and evidence of PC double bond formation

2018 ◽  
Vol 47 (25) ◽  
pp. 8402-8417 ◽  
Author(s):  
Lukas Keweloh ◽  
Niklas Aders ◽  
Alexander Hepp ◽  
Damian Pleschka ◽  
Ernst-Ulrich Würthwein ◽  
...  
Keyword(s):  
Double Bond ◽  
Ring Opening ◽  
Bond Formation ◽  
Frustrated Lewis Pair

A P–H functionalized FLP reacted with RX-CN by hydrophosphination. Ring opening by treatment with cyclopropenthione resulted in PC bond formation.

Model Compounds Related to Saquayamycin. Attempts to Oxygenate the A/B Ring Junction

2002 ◽  
Vol 55 (5) ◽  
pp. 343 ◽  
Author(s):  
M. A. Apponyi ◽  
J. H. Bowie ◽  
B. W. Skelton ◽  
A. H. White
Keyword(s):  
Double Bond ◽  
Maleic Anhydride ◽  
Good Yield ◽  
Ring Opening ◽  
Diels Alder ◽  
Aromatic System ◽  
Model Compounds ◽  
Similar Treatment ◽  
Ring Junction

The aim of this project was to attempt to find a method for introducing the cis-dihydroxyl substitution at the A/B-ring junction of model compounds related to the saquayamycins. The Diels-Alder reactions of maleic anhydride and bromomaleic anhydride with 5,5-dimethyl-3-vinylcyclohexa-1,2-dienyl acetate gave the two required endo-adducts in good yield, namely (octahydrobenzo[e]isobenzofuran-9-yl acetate (6) and (octahydrobenzo[e]isobenzofuran-9-yl acetate (9). Each of these was converted into the B-ring mono-epoxide, namely (H-benzo[e]oxireno-2,3-furan-1-yl acetate (7) and a mixture of two racemic diastereoisomers of 9a-bromo-3,3-dimethyl-7,9-dioxoperhydrobenzo[e]oxi- reno[2,3-f]isobenzofuran-1-yl acetate (12), respectively. It was then hoped to deprotonate both (7) and (12) at the 9a position in order to effect migration of the 8,9 double bond to the 9,9a position. Reaction of (7) with a mild base (pyridine) did not effect any reaction. Similar treatment of (12) did remove the 9a proton, but it also effected ring opening of the epoxide, followed by dehydration and dehydrobromination to give an excellent (but unwanted) yield of the aromatized system (±)-7,7-dimethyl-1,3-dioxo-1,3,5,7-tetrahydrobenzo (e]isobenzofuran-9-yl acetate. Dehydrobromination of (9), and deprotonation of the 9a position, similarly formed the aromatic system (e]isobenzofuran-9-yl acetate (11) in good yield.

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