24567-27-9Relevant articles and documents
Fast Addition of s-Block Organometallic Reagents to CO2-Derived Cyclic Carbonates at Room Temperature, Under Air, and in 2-Methyltetrahydrofuran
Elorriaga, David,de la Cruz-Martínez, Felipe,Rodríguez-álvarez, María Jesús,Lara-Sánchez, Agustín,Castro-Osma, José Antonio,García-álvarez, Joaquín
, p. 2084 - 2092 (2021/04/02)
Fast addition of highly polar organometallic reagents (RMgX/RLi) to cyclic carbonates (derived from CO2 as a sustainable C1 synthon) has been studied in 2-methyltetrahydrofuran as a green reaction medium or in the absence of external volatile organic solvents, at room temperature, and in the presence of air/moisture. These reaction conditions are generally forbidden with these highly reactive main-group organometallic compounds. The correct stoichiometry and nature of the polar organometallic alkylating or arylating reagent allows straightforward synthesis of: highly substituted tertiary alcohols, β-hydroxy esters, or symmetric ketones, working always under air and at room temperature. Finally, an unprecedented one-pot/two-step hybrid protocol is developed through combination of an Al-catalyzed cycloaddition of CO2 and propylene oxide with the concomitant fast addition of RLi reagents to the in situ and transiently formed cyclic carbonate, thus allowing indirect conversion of CO2 into the desired highly substituted tertiary alcohols without need for isolation or purification of any reaction intermediates.
Alkyl Group Effects on the Rate Constants and Equilibrium Constants for Formation of Cyclic Tetrahedral Intermediates
Santry, Linda J.,Azer, Salwa,McClelland, Robert A.
, p. 2909 - 2914 (2007/10/02)
2-Hydroxy-2-alkyl-1,3-dioxolanes T are the cyclic intermediates of the degenerate intramolecular ester interchange reactions of ethylene glycol monoalkanoates A, in which alkanoyl groups transfer from one end of ethylene glycol to the other.This study reports equilibrium constants for the cyclization AT to the tetrahedral intermediate stage with 10 alkanoate derivatives.These equiilibrium constants, which when written as / are all large (1 E7-1 E9) in favor of the ring opened form, were obtained as the ratio of rate constants for equilibration occuring with H+ catalysis.Rate constants for the ring opening of T were directly measured through a study of kinetics of the hydrolysis of 2-methoxy-2-alkyl-1,3-dioxolane ortho esters.These hydrolysis proceed via T, and under acid conditions the breakdown of this intermediate is rate-limiting.Rate constants in the ring-closing direction were obtained by preparing HOCH2CD2OOCR and, with the use of 1H NMR spectroscopy, measuring the kinetics of isomerization to an equilibrium mixture with RCOOCH2CD2OH.The reaction under investigation is an intramolecular analogue of H+-catalyzed alkanoate ester hydrolysis, whose rate constant define the steric substituent parameter Es.The ring-closure rate constant for A -> T do show an excellent correlation with Es.However, the rate constants for ring-opening T -> A and the overall equilibrium constant are badly correlated, showing quite different behavior for series with α and β branching in the alkyl group.Thus, for this system the Es parameter does not correlate free energy differencies between the acyl derivative and tetrahedral intermediate.It is only the free energy differences between the acyl form and the transition state leading to the intermediate that fit Es.
