Gold(I)-Catalyzed Polycyclization of Linear Dienediynes to Seven-Membered Ring-Containing Polycycles via Tandem Cyclopropanation/Cope Rearrangement/C–H Activation

2014 ◽  
Vol 16 (22) ◽  
pp. 5898-5901 ◽  
Author(s):  
Pei-Jun Cai ◽  
Yi Wang ◽  
Cheng-Hang Liu ◽  
Zhi-Xiang Yu
Keyword(s):  
Membered Ring ◽  
Cope Rearrangement

The Takayama Synthesis of (-)-Cernuine

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Tertiary Amine ◽  
Membered Ring ◽  
The Other ◽  
Cope Rearrangement ◽  
Acryloyl Chloride ◽  
The Core ◽  
Diastereoselective Addition ◽  
Lactam Carbonyl ◽  
Acidic Conditions ◽  
Stereogenic Center

(-)-Cernuine 3 falls in the subset of the Lycopodium alkaloids that feature a bicyclic aminal core. There had not been a total synthesis of this class of alkaloids until the recent (Organic Lett. 2008, 10, 1987) work of Hiromitsu Takayama of Chiba University. The key step in this synthesis was a diastereoselective intramolecular reductive amination, converting 1 to 2. As is apparent from the 3-D projection, (-)-cernuine 3 has a tricyclic trans-anti-trans aminal core, with an appended six-membered ring, both branches of which are axial on the core. While the branch that is part of the aminal could be expected to equilibrate, the other branch had to be deliberately installed. The synthesis began with (+)-citronellal 4, each enantiomer of which is commercially available in bulk. After protection and ozonolysis, the first singly-aminated stereogenic center was installed by enantioselective, and therefore diastereoselective, addition of 5 to the azodicarboxylate 6, mediated by the organocatalyst 7. Reductive cleavage of the N-N bond followed by acetal methanolysis converted 8 to 9. Ionization followed by allyl silane addition then delivered 11, having the requisite axial alkyl branch. The next two tasks were the assembly of the second of the four rings of 3, and the construction of the second single-aminated stereogenic center. The ring was assembled by deprotection of 11 followed by acylation with acryloyl chloride, to give 12. Grubbs cyclization followed by hydrogenation then led to 13. Homologation of 13 to the aldehyde 14 set the stage for condensation with the camphor-derived tertiary amine 15, following the protocol developed by Kobayashi. Sequential imine formation, aza-Cope rearrangement, and hydrolysis led to 1 in 94% de. One could envision reduction of the lactam carbonyl of 1 to an aldehyde equivalent, that would then, under acidic conditions, condense to form the desired aminal 2. This approach was, however, not successful. As an alternative, conditions were developed to convert 1 to the amidine 16. Reduction then proceeded with the expected high diastereocontrol, to give the cis 1,3-fused aminal 2. This was not isolated, but was directly acylated with acryloyl chloride, to 17.

Seven-membered ring annulation and spiro-annulation processes via preparation and thermal rearrangement of β-(2-vinylcyclopropyl) α,β-unsaturated ketones

1983 ◽  
Vol 61 (6) ◽  
pp. 1226-1238 ◽  
Author(s):  
Edward Piers ◽  
Howard E. Morton ◽  
Isao Nagakura ◽  
Richard W. Thies
Keyword(s):  
Elevated Temperatures ◽  
Phase Transfer ◽  
Major Product ◽  
Sigmatropic Rearrangement ◽  
Membered Ring ◽  
Minor Amount ◽  
Pyridinium Chlorochromate ◽  
Cope Rearrangement ◽  
Thermal Rearrangement ◽  
Unsaturated Ketones

Treatment of the β-iodo enones 4 and 26–28 with lithium (phenylthio)(2-vinylcyclopropyl)cuprate (21, mixture of epimers), followed by thermolysis (180 °C, 30–45 min) of the initially formed β-(2-vinylcyclopropyl) enones, provided excellent yields of the seven-membered ring annulation products 25 and 30–32, respectively. In similar fashion, the (E)-2-(iodomethylene)cycloalkanones 8 and 29 were transformed efficiently into the spiro-annulation products 34 and 35 respectively. When compound 36 was treated with bromoform – sodium hydroxide in the presence of a phase-transfer catalyst, the dibromocyclopropane 37 was produced. The latter substance served as the starting material for a sequence of reactions (hydrolysis with hydrochloric acid in methanol, 37 → 38; oxidation with pyridinium chlorochromate, 38 → 39; Wittig reaction with methylenetriphenylphosphorane, 39 → 40; reduction with zinc in acetic acid, 40 → 41) culminating in the stereoselective formation of cis-1-bromo-2,2-dimethyl-3-vinylcyclopropane (41). On the other hand, treatment of compound 37 with n-butyllithium (ether, −90 °C), followed by protonation of the presumed intermediate 43 and hydrolysis of the resultant product 44, provided the bromo alcohol 45 in 70% yield. The latter substance was converted into trans-1-bromo-2,2-dimethyl-3-vinylcyclopropane (47). When the cuprate reagents 42 and 48 (prepared from the bromocyclopropanes 41 and 47, respectively) were allowed to react with the iodo enones 4 and 26, the β-(2-vinylcyclopropyl) α,β-unsaturated ketones 49, 52, 54, and 56 were produced in high yields. The enone 49, upon thermolysis in refluxing n-hexane, underwent facile Cope rearrangement to produce the annulation product 50 quantitatively. In contrast, the homolog 54 was notably resistant to [3,3]-sigmatropic rearrangement and, upon thermolysis in o-xylene, o-dichlorobenzene, or collidine at elevated temperatures produced, in varying ratios, the Cope rearrangement product 55 and the isomerization product 56. Thermal rearrangement (o-dichlorobenzene, 220 °C, sealed tube) of trans-3-(2,2-dimethyl-3-vinylcyclopropyl)-2-cyclohexen-1-one (52) provided the annulation product 51 (59% yield). In contrast, the corresponding homolog 56, under very similar conditions, produced only a minor amount of the annulation product 55. In this case, the major product (trienone 57) was that resulting from a [1,5]-sigmatropic hydrogen migration (ratio of 55/57 ≈ 1:4).

Synthesis of 7-Membered Ring Carbocycles via a Palladium-Catalyzed Intramolecular Allylic Alkylation-Isomerization-Cope Rearrangement Cascade

2018 ◽  
Vol 2018 (22) ◽  
pp. 2836-2840 ◽  
Author(s):  
Kazuki Tsuruda ◽  
Takahisa Tokumoto ◽  
Naoya Inoue ◽  
Masaya Nakajima ◽  
Tetsuhiro Nemoto
Keyword(s):  
Membered Ring ◽  
Cope Rearrangement ◽  
Allylic Alkylation ◽  
Palladium Catalyzed

An Alternate Energy-Conserved Pathway for the Morita-Baylis-Hillman (MBH) Reaction

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Lower Energy ◽  
Aldol Reaction ◽  
Membered Ring ◽  
Ammonium Ion ◽  
Alternate Energy ◽  
Ring Transition State ◽  
Mbh Reaction

An new overall lower energy pathway for the amine-catalysed Morita-Baylis-Hillman reaction is proposed from computations at the M06-2X/6-311++G(d,p) level. The pathway involves proton-transfer from the ammonium ion to the alkoxide formed from the aldol reaction through a seven-membered ring transition state (TS) structure followed by highly exothermic Hofmann<i> </i>elimination through a five-membered ring TS structure to form the product and also release the catalyst to carry on with the process all over again.

An Alternate Energy-Conserved Pathway for the Morita-Baylis-Hillman (MBH) Reaction

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Lower Energy ◽  
Aldol Reaction ◽  
Membered Ring ◽  
Ammonium Ion ◽  
Alternate Energy ◽  
Ring Transition State ◽  
Mbh Reaction

An new overall lower energy pathway for the amine-catalysed Morita-Baylis-Hillman reaction is proposed from computations at the M06-2X/6-311++G(d,p) level. The pathway involves proton-transfer from the ammonium ion to the alkoxide formed from the aldol reaction through a seven-membered ring transition state (TS) structure followed by highly exothermic Hofmann<i> </i>elimination through a five-membered ring TS structure to form the product and also release the catalyst to carry on with the process all over again.

Catalytic Synthesis of Cyclic Guanidines via Hydrogen Atom Transfer and Radical-Polar Crossover

2020 ◽  
Author(s):  
Shunya Ohuchi ◽  
Hiroki Koyama ◽  
Hiroki Shigehisa
Keyword(s):  
Hydrogen Atom ◽  
Functional Group ◽  
Hydrogen Atom Transfer ◽  
Catalytic Synthesis ◽  
Membered Ring ◽  
Biologically Active ◽  
Atom Transfer ◽  
Powerful Method ◽  
Protective Groups ◽  
The Common

A catalytic synthesis of cyclic guanidines, which are found in many biologically active compounds and natu-ral products, was developed, wherein transition-metal hydrogen atom transfer and radical-polar crossover were employed. This mild and functional-group tolerant process enabled the cyclization of alkenyl guanidines bearing common protective groups, such as Cbz and Boc. This powerful method not only provided the common 5- and 6-membered rings but also an unusual 7-membered ring. The derivatization of the products afforded various heterocycles. We also investigated the se-lective cyclization of mono-protected or hetero-protected (TFA and Boc) alkenyl guanidines and their further derivatiza-tions.

Convergent Total Synthesis of Principinol D, a Rearranged Kaurane Diterpenoid

2019 ◽  
Author(s):  
Timothy Newhouse ◽  
Aneta Turlik ◽  
Yifeng Chen ◽  
Anthony Scruse
Keyword(s):  
Total Synthesis ◽  
Natural Product ◽  
Late Stage ◽  
Membered Ring ◽  
Entry Point ◽  
Ketone Reduction ◽  
Coupling Approach

<div> <p>The total synthesis of principinol D, a rearranged kaurane diterpenoid, is reported. This grayanane natural product is constructed via a convergent fragment coupling approach, wherein the central 7-membered ring is synthesized at a late stage. The bicyclo[3.2.1]octane fragment is accessed by a Ni-catalyzed α-vinylation reaction. Strategic reductions include a diastereoselective SmI<sub>2</sub>-mediated ketone reduction with PhSH and a new protocol for selective ester reduction in the presence of ketones. The convergent strategy reported herein may be an entry point to the larger class of kaurane diterpenoids.</p> </div>

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