Using Ring Strain to Control 4π-Electrocyclization Reactions: Torquoselectivity in Ring Closing of Medium-Ring Dienes and Ring Opening of Bicyclic Cyclobutenes

Highly functionalized and annulated 2,4-cyclooctadienones are formed in a stereoselective manner by sequential treatment of squarate esters with a lithiated enecarbamate (six-membered ring or larger) and a cycloalkenyl- or 1-alkenyllithium reagent. The mechanistic details of this multistep process are presented. Particular attention is drawn to the step that involves intramolecular nucleophilic attack by a proximal oxido anion at the carbamate carbonyl and results in redirection of the cascade. This step is thwarted when five-membered cyclic enecarbamates are employed because of the excessive buildup of ring strain in the associated transition state.Key words: squarate esters, enecarbamates, conrotatory ring opening, intramolecular acylation, alkenyllithium reagents.

Download Full-text

ChemInform Abstract: Directed Ring Opening of Oxiranylcarbinyl Radicals in the Synthesis of Medium Ring Carbocycles and Oxygen Heterocycles.

ChemInform ◽

10.1002/chin.199342212 ◽

2010 ◽

Vol 24 (42) ◽

pp. no-no

Author(s):

D. A. CORSER ◽

B. A. MARPLES ◽

R. K. DART

Keyword(s):

Ring Opening ◽

Oxygen Heterocycles ◽

Medium Ring

Download Full-text

Directed Ring Opening of Oxiranylcarbinyl Radicals in the Synthesis of Medium Ring Carbocycles and Oxygen Heterocycles

Synlett ◽

10.1055/s-1992-21557 ◽

1992 ◽

Vol 1992 (12) ◽

pp. 987-989 ◽

Cited By ~ 23

Author(s):

David A. Corser ◽

Brian A. Marples ◽

R. Kinsey Dart

Keyword(s):

Ring Opening ◽

Oxygen Heterocycles ◽

Medium Ring

Download Full-text

Ring-opening reactions. 3. Mechanistic path vs. ring-strain control in elimination and substitution reactions of 1,1-dimethyl cyclic ammonium ions and their .alpha.,.alpha.'-dimethyl-substituted derivatives

The Journal of Organic Chemistry ◽

10.1021/jo00327a021 ◽

1981 ◽

Vol 46 (14) ◽

pp. 2944-2947 ◽

Cited By ~ 25

Author(s):

Gabriella Cospito ◽

Gabriello Illuminati ◽

Claudio Lillocci ◽

Horia Petride

Keyword(s):

Ring Opening ◽

Ammonium Ions ◽

Substitution Reactions ◽

Strain Control ◽

Ring Strain ◽

Ring Opening Reactions

Download Full-text

Electron-donating groups and high ring strain promoted ring opening of methylenecyclopropanes catalyzed by rhodium and iridium complexes

Journal of Organometallic Chemistry ◽

10.1016/j.jorganchem.2016.03.006 ◽

2016 ◽

Vol 811 ◽

pp. 29-39 ◽

Cited By ~ 1

Author(s):

Xiangai Yuan ◽

Wenmin Wang ◽

Ziqi Tian ◽

Siwei Bi ◽

Jing Ma

Keyword(s):

Ring Opening ◽

Iridium Complexes ◽

Ring Strain ◽

Electron Donating Groups

Download Full-text

Cationic ring-opening polymerization of cyclic carbonates and lactones by group 4 metallocenes: A theoretical study on mechanism and ring-strain effects

Journal of Theoretical and Computational Chemistry ◽

10.1142/s0219633617500031 ◽

2017 ◽

Vol 16 (01) ◽

pp. 1750003 ◽

Cited By ~ 5

Author(s):

Jitrayut Jitonnom ◽

Wijitra Meelua

Keyword(s):

Ring Opening ◽

Density Functional ◽

Bond Cleavage ◽

Mechanistic Study ◽

Chain Growth ◽

Ring Size ◽

Cyclic Carbonates ◽

Complex Catalyst ◽

Ring Strain ◽

Group 4

Group 4 metallocene-mediated cationic ring-opening polymerizations of a series of lactones and cyclic carbonates, with different ring sizes ([Formula: see text]–8) have been theoretically studied. Using the “naked cation” approach in combination with density functional theory, the activated chain-end mechanism and the influence of transition metals, solvent and monomer ring size on the polymerizability were explored in detail. The results showed that the cationic metallocene–monomer complex, [catalyst][monomer][Formula: see text], is formed, generating cationic (carbocation ion) species responsible for polymer chain growth. We found that poor polymerizability of five-membered lactone and six-membered ring carbonate depends not only on the nature of the monomer ring size but also the relative stability of the complex, which was found to correlate well with the ring strain. Subsequently, several propagation steps take place through an SN2 reaction which involves ring opening of an active monomer, via alkyl–oxygen bond cleavage. Based on the computed activation energies of all metallocene systems, the first propagation was found to be the rate-determining step of the overall propagation and the hafnocene was found to be most active with the energy barrier of 17.6[Formula: see text]kcal/mol, followed by zirconocene (18.6[Formula: see text]kcal/mol) and titanocene (19.5[Formula: see text]kcal/mol), respectively. The mechanistic study may be applicable to the cationic ROP of lactides and other related monomers.

Download Full-text