Novel modes of generation and reactivity of arynes and 1,2,4-cyclohexatrienes from acyclic precursors

Abstract

The hexadehydro-Diels–Alder (HDDA) cycloisomerization between a tethered diyne and diynophile forms an intermediate aryne, providing chemists with a tool to simultaneously form new aromatic rings and add chemical complexity to the ring in one operation. In contrast, the tetradehydro-Diels–Alder (TDDA) reaction between a tethered enyne and alkyne generates a useful, strained intermediate (1,2,4-cyclohexatriene), but in most cases lacks the ability to trap external reagents due to rapid aromatization. My scientific contribution to generating and trapping reactive intermediates resultant from a cyclization event falls into three categories i) divergent reactivity of HDDA arynes relative to classically generated methods, ii) rapid generation of HDDA arynes at room temperature, and iii) modification of TDDA precursors to allow for trapping of the resultant intermediate. My initial work focuses on studying the reaction of HDDA arynes with phosphine sulfides and selenides to afford helical dibenzothiophenes and selenophenes via a rare, pentavalent P(V) intermediate (Chapter 2). Next, a study on HDDA arynes with 1,3,4-oxadiazoles revealed a novel mode of producing 2:1 adducts, eventually leading to my discovery of the first dearomatized product arising from an HDDA process (Chapter 3). While these studies focused on novel trapping modes, I shifted my attention to a study of anhydride-linked HDDA precursors, leading to the discovery of a remarkable rate enhancement of cyclization (Chapter 4). Finally, I pursued a study on a less explored class of intermediates – 1,2,4-cyclohexatrienes – in which an unprecedented mode of trapping is reported (Chapter 5).