Synthesis of α-Substituted Vinylsulfonium Salts and Their Application as Annulation Reagents in the Formation of Epoxide- and Cyclopropane-Fused Heterocycles

Abstract

The discovery of new methods for the synthesis of classes of potentially bioactive molecules remains an important goal for synthetic chemists. Vinylsulfonium salts have been used for the synthesis of a wide variety of small heterocyclic motifs; however, further developments to this important class of reagents has been focused on reaction with new substrates rather than development of new vinylsulfonium salts. We herein report the synthesis of a range of α-substituted vinylsulfonium tetraphenylborates (10 examples) in a 3 step procedure from commercially available styrenes. The important role of the tetraphenylborate counterion on the stability and accessibility of the vinylsulfonium salts is also detailed. The α-substituted vinylsulfonium tetraphenylborates gave good to excellent yields in the epoxyannulation of β-amino ketones (15 examples) and the cyclopropanation of allylic amines (4 examples). Hydrogenation of an epoxyannulation product proceeded with good diastereoselectivity.

Bypassing the Inertness of Aziridine/CO2 Systems to Access 5‐Aryl‐2‐Oxazolidinones: Catalyst‐Free Synthesis Under Ambient Conditions

“…Thus, an excess of carbamate (from NH 2 iPr/CO 2 ) in aqueous solution was added to the precursor (1 and 4, respectively) in D 2 O in an NMR tube. 1 H and 2D-HMBC experiments revealed the progressive formation of (1-arylvinyl)dimethylsulfonium salts (VS1, VS4), [29] promoted by the basicity of the carbamate (Scheme 2, step i). This finding is in alignment with previous reports on the reactivity of 1 with Brønsted bases.…”

Recent Developments in Vinylsulfonium and Vinylsulfoxonium Salt Chemistry

“…Aggarwal and co-workers later introduced α -substituted vinylsulfonium tetraphenylborates 98 as stable isolable salts [ 53 ]. Epoxy annulation reactions of the α -substituted vinylsulfonium tetraphenylborates 98 with α -amino ketones 81 gave bicyclic expoxy-fused heterocycles 99 in good yields and with high diastereoselectivity ( Scheme 31 ).…”

Copper Promoted Oxidative Coupling of SnAP Hydrazines and Aldehydes to Form Chiral 1,4,5‐Oxadiazepanes and 1,2,5‐Triazepanes

“…Saturated nitrogen heterocycles have attracted considerable attention due to their wide range of pharmacological activities . A number of modern methods are devoted to their construction and impressive progress in hydroamination, C–H functionalization, α ‐lithiation, or annulation methodologies have improved access to these structures. To this end, our group has introduced SnAP (Sn (tin) amine protocol) reagents, and SLAP (silicon amine protocol) reagents for the one‐step transformation of aldehydes and ketones to saturated, substituted, N‐unprotected aza‐heterocycles as thiomorpholines, morpholines, piperazines, piperidines, pyrrolidines, medium‐sized rings, and spirocycles.…”