A Journey Through the Chemistry of Reactive Intermediates: From a Trimethylenemethane Diyl to Electrochemically-Generated Radical Ions.

摘要

Reactive intermediates, such as those derived from trimethylenemethane (TMM) diyls or electrochemically-generated radical ions, provide a versatile platform for exploring a wide variety of unique and interesting chemistries. A particular emphasis is placed on gaining a fundamental understanding of these intermediates through (a) mechanistic investigations or (b) method development, both of which are discussed herein. Unlike the reaction of aryl-substituted diazenes, pyrolysis of alkyl-substituted diazenes in the presence of molecular oxygen generates an unexpectedly complex product mixture. Using deuterium labeling studies, in conjunction with quantum calculations, a reasonable mechanistic hypothesis for the decomposition of the resultant [3.3.0] peroxide, and subsequent formation of the keto-alcohol and Z-configured alpha,beta-unsaturated keto-aldehyde, is proposed. Surprisingly, molecule-assisted homolysis plays a key role in this transformation, the details of which are discussed. While fulvenes have a rich history taking advantage of their aromatic and olefinic characteristics, very little is known about the electrochemical properties of these compounds. One interesting aspect of their electrochemical behavior--the elecroreductive cyclization of a fulvene tethered to an alpha,beta-unsaturated ester--is examined. In particular, the details concerning directed product formation via temperature control and concentration effects toward dimerization, or toward cyclization through a variation of the length of the tether joining the fulvene core to the second electrophore are discussed. Indirect electron transfer using electrochemical mediators allows many reactions to be run under milder redox conditions, e.g. requiring less total energy consumption. Unfortunately, in the majority of cases the mediators can't be recovered; therefore a recoverable mediator source would be both economically and ecologically attractive. Taking advantage of a generally underappreciated tool in organic electrochemistry, viz., the electrode surface, progress towards the modification of electrode surfaces with mediator-functionalized terthiophene polymers is presented. The aim of the investigation is to provide a method to recover and reuse electrochemical mediators, and thus a sustainable alternative to traditional mediated electrochemistry. One application of interest that will be explored is the anodic oxidative degradation of lignin model compounds.