Reaction of 1-aryl-2-methylenecyclopropanes with rhodium(I) complexes leading to ring opening isomerization and π co-ordination of the CC double bond

1999 ◽  
pp. 853-860 ◽  
Author(s):  
Kohtaro Osakada ◽  
Hisami Takimoto ◽  
Takakazu Yamamoto
Keyword(s):  
Double Bond ◽  
Ring Opening

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.

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.

The preparation of a stable 8-oxatricyclo[4,3,0,07,9]nona-2,4-diene and an evaluation of its potential as a source for the photochemical generation of oxiren

1981 ◽  
Vol 34 (4) ◽  
pp. 855 ◽  
Author(s):  
RN Warrener ◽  
RA Russell ◽  
RYS Tan
Keyword(s):  
Hydrogen Peroxide ◽  
Double Bond ◽  
Photochemical Reaction ◽  
Ring Opening ◽  
Thermal Conditions ◽  
Ring System ◽  
Crystalline Solid ◽  
Mercuric Oxide ◽  
Azo Compound ◽  
Photochemical Generation

The synthesis of 2-methyl-3,4,5-triphenyl-8-oxatricyclo[4,3,0,07,9]nona-2,4-diene (14) is described, the first stable member of this ring system. Preparation of (14) was achieved by reacting dibenzyl diazenedicarboxylate with 2-methyl-3,4,5-triphenylbicyclo[4,2,0]octa-2,4,7-triene (29) to form the adduct (30a), which was selectively epoxidized at the cyclobutenyl double bond with 3-chloroperbenzoic to yield the epoxide (32a). Removal of the benzyl groups (H2/Pd) from the hydrazo bridge of (32a), followed by oxidation (red mercuric oxide or hydrogen peroxide) yielded the putative azo compound (33) which spontaneously lost dinitrogen, even at -78�, to yield (14) as a crystalline solid, m.p. 128�. While (14) has the potential to undergo 1,2-photoaromatization to yield oxiren (4a), this is not realized and ring-opening to the cyclic epoxide (34) is the major photochemical reaction observed under various ultraviolet irradiation conditions. Isomerization of (14) into (34) also occurs under thermal conditions. The 1H n.m.r, spectra of (14) as well as its trapping with dienophiles is discussed.

scholarly journals Torquoselectivity of the Ring-Opening Reaction of 3,3-Dihalosubstituted Cyclobutenes: Lone Pair Repulsion and Cyclic Orbital Interaction

2019 ◽  
Author(s):  
Yuji Naruse ◽  
Atsushi Takamori
Keyword(s):  
Double Bond ◽  
Ring Opening ◽  
Lone Pair ◽  
Repulsive Interaction ◽  
Orbital Interaction ◽  
Ring Opening Reaction ◽  
Ring Opening Reactions ◽  
Major Factors ◽  
Vacant Orbital ◽  
Model Reactions

<div><div>Three major factors determine torquoselectivity, which is the diastereoselectivity in electrocyclic ring-opening reactions to produce <i>E</i>/<i>Z</i>-double bond(s). One is the interaction between the decomposing s<sub>CC</sub> bond and low-lying vacant orbital(s), such as a p*- or s*-orbital on the substituent, which promotes the reaction, resulting in inward rotation of the substituent. Second, for a substituent with a lone pair(s), repulsive interaction between the decomposing s-bond and the lone pair(s) hinders inward rotation, so that the products of outward rotation should be preferred. Finally, a more strongly donating s-electron-donating group (sEDG) rotates inwardly due to stabilization by phase-continuous cyclic orbital interaction. We compared the latter two interactions, repulsion between the lone pairs on the substituent and stabilization from phase-continuous cyclic orbital interaction, to determine which has a greater effect on the diastereoselectivity. We considered a series of model reactions with halogen substituents, and concluded that the diastereoselectivity is mainly controlled by cyclic orbital interaction.<br></div></div>

Cobalt-Mediated [2+2+2] Cycloadditions of Alkynes to Benzo­-[b]furans and Benzo[b]thiophenes: A Potential Route toward Morphanoids

Synthesis ◽  
2017 ◽  
Vol 50 (05) ◽  
pp. 1053-1089 ◽  
Author(s):  
K. Vollhardt ◽  
Tobias Aechtner ◽  
David Barry ◽  
Ellen David ◽  
Cédric Ghellamallah ◽  
...  
Keyword(s):  
Double Bond ◽  
Ring Opening

Exploratory studies of the CpCo-mediated [2+2+2] cycloaddition of alkynes to the 2,3-double bond of benzo[b]furans (and some benzo[b]thiophenes) are presented, with the general aim to access morphinan substructures. The basic feasibility of constructing Co-complexed tetrahydrophenanthro[4,5-bcd]furans (and -thiophenes) in moderate to good yields is demonstrated, with complete to extensive diastereoselectivity. Limitations are the apparent necessity for bulky (silylated) monoalkynes, the lack of regioselectivity in the cocyclization with unsymmetrical alkynes, and the sensitivity of the ligands, both complexed and uncomplexed, with respect to ring opening and rearrangement.

Cyclopropanation of benzylidenemalononitrile with dialkoxycarbenes and free radical rearrangement of the cyclopropanes

2001 ◽  
Vol 79 (3) ◽  
pp. 312-318
Author(s):  
Nadine Merkley ◽  
Paul C Venneri ◽  
John Warkentin
Keyword(s):  
Free Radical ◽  
Double Bond ◽  
Rate Constant ◽  
Ring Opening ◽  
Radical Addition ◽  
Radical Pairs ◽  
Radical Chemistry ◽  
Radical Rearrangement ◽  
Benzyl Radicals

Thermolysis of 2-cinnamyloxy-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (1a) and the analogous 2-benzyloxy-2-methoxy compound (1b) at 110°C, in benzene containing benzylidenemalononitrile, afforded products of apparent regiospecific addition of methoxycarbonyl and cinnamyl (or benzyl) radicals to the double bond. When the thermolysis of 1a was run with added TEMPO, methoxycarbonyl and cinnamyl radicals were captured. Thermolysis of the 2,2-dibenzyloxy analogue (1c) in the presence of benzylidenemalononitrile gave an adduct that is formally the product of addition of benzyloxycarbonyl and benzyl radicals to the double bond. In this case, a radical addition mechanism could be ruled out, because the rate constant for decarboxylation of benzyloxycarbonyl radicals is very large. A mechanism that fits all of the results is predominant cyclopropanation of benzylidenemalononitrile by the dialkoxycarbenes derived from the oxadiazolines, in competition with fragmentation of the carbenes to radical pairs. The cyclopropanes so formed then undergo homolytic ring-opening to the appropriate diradicals. Subsequent β-scission of the diradicals to afford radical pairs, and coupling of those pairs, gives the final products. Thus, both carbene and radical chemistry are involved in the overall processes.Key words: cyclopropane, dialkoxycarbene, β-scission, oxadiazoline, radical.

Sign in / Sign up

Export Citation Format

Share Document