Synergistic Pd(0)/Rh(II) Dual Catalytic [6 + 3] Dipolar Cycloaddition for the Synthesis of Monocyclic Nine-Membered N,O-Heterocycles and Their Alder-ene Rearrangement to Fused Bicyclic Compounds

Abstract

The catalytic construction of a monocyclic medium-sized N,O-heterocyclic ring represents a formidable challenge in organic synthesis. Herein we report the synergistic palladium(0)/rhodium­(II) dual catalytic cycloaddition of vinylpropylene carbonates with N-sulfonyl-1,2,3-triazoles to afford monocyclic nine-membered N,O-heterocycles. The catalytically generated 1,6-dipole-equivalent zwitterionic π-allyl palladium­(II) complex and the 1,3-dipole-equivalent α-imino rhodium­(II) carbenoid intermediate react with each other in a formal [6 + 3] dipolar cycloaddition to furnish nine-membered oxazonines, which can be transformed into cis-fused [4.3.0] bicyclic compounds via a transannular Alder-ene rearrangement. The tandem one-pot cycloaddition/Alder-ene rearrangement sequence is also possible.

Recent Advances in the Synthesis of 5‐MemberedN‐Heterocycles via Rhodium Catalysed Cascade Reactions

“…Tandem one-pot synthesis of hexahydropyranopyrroles via an alder-ene rearrangement. [162] approach and dimerization of two molecules of 275 under the active Rh(III) catalyst to give a cyclic enamine intermediate E, which undergoes a tautomerization and aromatization to afford 277. 275 proceeded though a stepwise process to give 276 (Scheme 80).…”

“…They also revealed the transannular alder-ene rearrangement of the 1,4-oxazonines to furnish cisfused bicyclic hexahydropyranopyrroles 272 (Scheme 78). [162] The carbene/alkyne metathesis (CAM) cascade reactions have received considerable attention due to their extraordinary efficiency for complex molecular synthesis. [163a] The key transformations of metal carbenes and secondary amides include NÀ H insertion and OÀ H insertion reactions.…”

“…They also revealed the transannular alder‐ene rearrangement of the 1,4‐oxazonines to furnish cis‐fused bicyclic hexahydropyranopyrroles 272 (Scheme 78). [162] …”

“…Scheme 78. Tandem one-pot synthesis of hexahydropyranopyrroles via an alder-ene rearrangement [162]. …”

Recent Advances in Decarboxylative Conversions of Cyclic Carbonates and Beyond

“…abled formal [6+3] cycloadditions between VCCs and N-sulfonyl-1,2,3-triazoles, resulting in monocyclic nine-membered N,O-heterocycles. 7 In 2020, Han and co-workers 8 developed Pd-catalyzed regiodivergent [5+4] and [5+2] annulations between VCCs and allylidenemalononitriles (Scheme 5). These interesting conversions could be used for the synthesis of several medium-sized heterocycles, which are otherwise synthetically quite challenging but useful.…”