Efficient Synthesis of 4,7-Dihydro-1H-oxepino[2,3-c]pyrazoles by Potassium Carbonate Promoted [4+3] Annulation of Crotonate-Derived Sulfur Ylides with Benzylidenepyrazolones

Abstract

The [4+3] annulation reaction of crotonate-derived sulfur ylides with benzylidenepyrazolones using K2CO3 as the base is reported. The ready availability of starting materials and the simple cyclization procedure make this approach suitable for the preparation of a diverse array of 4,7-dihydro-1H-oxepino[2,3-c]pyrazoles in good to excellent yields.

Regioselective N-Addition/Substitution Reaction of α-Alkylidene Pyrazolinones with Propargyl Sulfonium Salts to Construct Allylthio-Containing Pyrazolones

“…Several key observations should be noted. First, compared to the stoichiometric quantity of base (2.0 or 3.0 equiv) in previous reports of propargyl sulfonium salts, − 0.5 equiv of the base was sufficient to furnish the reaction. Next, the reaction was an obvious stepwise process and α-alkylidene pyrazolinone 1a was consumed completely within 5 min at 22 °C while the amount of product 3a was in trace (monitored by TLC).…”

“…Sulfur ylides are valuable synthons and have wide applications in a variety of transformations such as olefination, cyclopropanation, epoxidation, aziridination, and rearrangement reactions. , Particularly, propargyl sulfonium salts are a kind of versatile building blocks that are easily accessible and convenient to access functional cyclic skeletons because of multiple reaction centers. Generally, propargyl sulfonium salts can tautomerize to allenic sulfonium salts under basic conditions, including three reactive sites of α-carbon, β-carbon, and α′-carbon (Scheme ).…”

Recent Advances on Annulation Reactions with Allyl and Propargyl Sulfonium Salts

“…For instance, Miao and co-workers applied the [4+3] cyclization strategy in reactions with benzylidene pyrazolones 22, providing access to pyrazole-fused seven-membered rings (Scheme 13, A). 21 Various pyrazolone-derived enones 22 bearing aromatic substituents could efficiently participate in this annulation, whilst a ,-dimethyl-substituted enone was also a suitable substrate which gave the corresponding product in a moderate yield.…”