Synthetic Applications of Intramolecular Insertion in Arylcarbenes. III. Generation and Rearrangement of Aryloxycarbenes by Intramolecular Abstraction of Hydrogen

Abstract

o-Alkoxy- and o-alkylthio-phenylcarbenes, generated by low-pressure pyrolysis in the gas phase, show abstraction of 2H across space to generate the corresponding o-tolyl vinyl ethers or sulfides. In the case of o-ethoxyphenylcarbene, deuterium labelling shows that this is a case of vicinal abstraction, not geminal abstraction followed by 1,2-hydride shift. o-Methoxyphenylcarbene, however, is similarly shown to undergo geminal hydrogen abstraction leading to o-tolyloxycarbene, which undergoes a 1,2-aryl shift to give o-tolualdehyde. Independent generation of aryloxycarbenes has been achieved by pyrolysis of 5-aryloxy-2,2-dimethyl-l,3-dioxan- 4,6-diones. The product carbenes show the expected rearrangement as well as normal insertion reactions.