Generation of Arynes via Ate Complexes of Arylboronic Esters with an ortho-Leaving Group
摘要:
An efficient method of generating aryne has been achieved by treating ortho-(trifluoromethanesulfonyloxy)arylboronic acid pinacol ester with tert-or sec-butyllithium. Monitoring the reaction by B-11 NMR has indicated that a boron-ate complex formed in situ is the eventual precursor that converts into aryne near room temperature. The prior formation of the ate complex at a low temperature has enabled us to use various arynophiles, including those bearing base-sensitive groups. The ready availability of the aryne precursors and mutual orthogonality in aryne generation with widely used ortho-silylaryl triflate have enhanced the utility of the method.
In the presence of a gold catalyst, the ring opening of 1,4-epoxy-1,4-dihydronaphthalenes with allyltrimethylsilane affords allylnaphthalenes in high yield. For unsymmetrical substrates, high regioselectivity is observed in many cases. This reaction might proceed via tricyclic tetrahydrofuran intermediates which are formed stereoselectively.