Organocatalytic Asymmetric Inverse-Electron-Demand Diels–Alder Reaction between Alkylidene Pyrazolones and Allyl Ketones: Access to Tetrahydropyrano[2,3-c]pyrazoles

Abstract

Herein we report a catalytic asymmetric inverse-electron-demand Diels–Alder reaction between alkylidene pyrazolones and allyl ketones. Allyl ketone gets activated by a bifunctional thiourea catalyst and acts as a dienolate in this reaction. The trisubstituted tetrahydropyrano[2,3-c]pyrazoles were obtained in moderate to good yields with high diastereo- and enantioselectivities. Few applications, including a decarbonylation reaction, have been demonstrated.

Diastereoselective Cascade Cyclization of Diazoimides with Alkylidene Pyrazolones for Preparation of Pyrazole-Fused Oxa-Bridged Oxazocines

“…Primarily, the cycloaddition of cyclic carbonyl ylides derived from diazoimides with structurally various dipolarophiles can be used to more efficiently and concisely deliver oxa-bridged heterocyclic scaffolds [31][32][33][34][35]. On the basis of the previous advances concerning the cyclization of carbonyl yildes [36][37][38][39][40], we envisioned the transition-metal catalyzed novel cascade cyclization of diazoimides 1 with alkylidenepyrazolones 2, which found a few examples of the cycloadditions centering on their enone moieties [41][42][43][44] (Scheme 1(2)). Pleasingly, in the presence of Rh 2 (OAc) 4 (10 mol%) and binapbisphosphine ligand (±)-L3 (20 mol%) in DCE at 80 • C, the newly designed cascade cyclization proceeded readily and diastereoselectively furnished pyrazole-fused oxa-bridged products 3 in reasonable chemical yields with excellent diastereoselectivities (>20:1 dr).…”