Metal‐Free Alkenylation of Salicylaldehydes with Boronic Acids: Synthesis of Skipped Dienes and 2H‐Chromenes

Abstract

Metal‐free alkenylation of salicylaldehydes and the preparation of 2H‐chromenes have been developed. Reactions occur in the presence of tetrafluoroboric acid diethyl ether complex. Vinylboronic acid derivatives including indeneboronic acid react readily with salicylaldehydes to afford the corresponding skipped dienes. When 6‐bromo or 6‐chlorosalicylaldehydes are submitted to the reaction conditions the formation of 2H‐chromenes is observed in good to excellent yields.

Catalyst-Controlled Divergent Synthesis of 2H-Chromenes via [3 + 3] Annulation of Vinyl Sulfoxonium Ylides with Quinones

“…According to the experimental results, our previous reports, 5b,c and other literature precedents, 11 undergoes the Michael addition reaction 5g,12 with the vinyl sulfoxonium ylide 1 at the γ-position followed by enolization and 1,3-isomerization to give the sulfoxonium salt 14. At this stage, the reaction may follow two paths.…”

“…According to the experimental results, our previous reports, , and other literature precedents, a possible mechanism was proposed for the 2 H -chromene-4-carboxylate 3 in Scheme a. Initially, Lewis acid activated quinone 2 undergoes the Michael addition reaction , with the vinyl sulfoxonium ylide 1 at the γ-position followed by enolization and 1,3-isomerization to give the sulfoxonium salt 14 .…”

“…At this stage, the reaction may follow two paths. In path A, the salt 14 can generate vinyl o -quinone methide intermediate 15 , which then undergoes oxa-6π-electrocyclization to furnish the chromene 3a . In path B, intramolecular nucleophilic displacement of DMSO by oxide ion in intermediate 14 can give 3a .…”

Divergent Reactivity of α,α-Disubstituted Alkenyl Hydrazones: Bench Stable Cyclopropylcarbinyl Equivalents

“…As a part of a research program centered on the synthesis of complex molecules that arise from terpene cyclase pathways, we required an efficient method to append a skipped diene unit onto aryl halides at the 3-position. , To that end, we sought to develop a fundamentally different approach inspired by the biosynthesis of 1,4-dienes (Figure B). Nature produces skipped dienes, like those found in irregular monoterpenes, through the sequential formation, ionization, and rearrangement of cyclopropylcarbinyl (CPC) pyrophosphates.…”