Rh-Catalyzed [3 + 2] Cycloaddition of 1-Sulfonyl-1,2,3-triazoles: Access to the Framework of Aspidosperma and Kopsia Indole Alkaloids

Abstract

A Rh(II)-catalyzed dearomative intramolecular [3 + 2] dipolar cycloaddition involving the indolic C2-C3 carbon-carbon double bond has been developed. The reaction was launched from the triazole moiety within the substrate and proceeded efficiently under mild conditions. A wide range of functional groups could be tolerated. These features render the current reaction a highly useful tool for the synthesis of polycyclic indole alkaloids, as showcased by a rapid assembly of the core structure of Aspidosperma and the related alkaloids.

Total Synthesis of Aspidosperma and Strychnos Alkaloids through Indole Dearomatization

“…Using this method, the authors synthesized (AE)-aspidophytine as wella ss everaln atural product analogues. [61] Notably,t he quite obvious possibility of using an enantioenricheds tarting materiali nt he cyclization cascade to achieve an asymmetric approachhas not been reported thus far.…”

Rhodium(II)‐Catalyzed Reaction of 1‐Tosyl‐1,2,3‐triazoles with Morita–Baylis–Hillman Adducts: Synthesis of 3,4‐Fused Pyrroles

“…Triazole chemistry has been extensively studied over the last decade, in which the N-sulfuryl-1,2,3-triazoles have been used as versatile synthetic precursors for the synthesis of nitrogencontaining heterocycles. [7][8][9][10][11] We have ag reat interesti na zaheterocycles ynthesis and N-sulfonyl-1,2,3-triazoles chemistry.W e have reported ap ractical and efficient method for divergent Scheme1.Rh II catalyzedreactionf or the construction of 3,4-fusedp yrroles.…”

“…Moreover, the use of 1,2-dichloroethane (DCE) or toluene as the solventd id not increase the yield of 3aa (entry [8][9]. The addition of Lewis acidh ave no positivee ffects (entry [10][11][12][13][14]. Finally, the reaction of MBH adduct 1a with 1.2 equiv of triazole 2a catalyzed by Rh 2 (Oct) 4 in CHCl 3 at 75 8Cw ere set as the optimum reaction conditions.…”

“…Gratifyingly,w ef ound that DBU promoted the cyclization smoothly to afford 4aa in 63 %y ield 1 [c] Rh 2 (OAc) 4 CHCl 3 -75 65 2 [c] Rh 2 (oct) 4 CHCl 3 -75 82 3 [c] Rh 2 (piv) 4 CHCl 3 -75 78 4 [c] Rh 2 (S-nttl) 4 CHCl 3 -75 67 5 [d] Rh 2 (oct) 4 CHCl 3 -75 86 6Rh 2 (oct) 4 CHCl 3 -75 90 [g] 7Rh 2 (oct) 4 CHCl 3 -85 88 8Rh 2 (oct) 4 CH 2 Cl 2 -75 77 9Rh 2 (oct) 4 toluene-75 73 (entry 7). Solvent effect was then tested with DBU as the base (entry [8][9][10][11]. The results show that the nonpolar solventt oluene is the best choice.M oreover, the yield did not increase either at ah igher reaction temperature or a lower reaction temperature (entry [12][13][14].W e envisioned that the additional oxidants would promote the reaction.…”

Radical Heterocyclization and Heterocyclization Cascades Triggered by Electron Transfer to Amide‐Type Carbonyl Compounds

“…[1] Developing expedient new methods to construct such systems is an important goal in synthetic and medicinal chemistry. [2] Fore xample,r ecent advances in the one-step construction of polycyclic systems possessing bridgehead nitrogen atoms include the [4+ +2]/[3+ +2] cycloaddition cascades of Boger, [3] therhodium(II)-catalyzed cyclization/[3+ +2] cycloaddition cascades of Padwa [4] and Zhai, [5] and Movassaghisd ouble intramolecular trapping of iminium ions. [1m] Perhaps because of the challenge associated with the control of selectivity in the reactions of highly reactive open-shell intermedates,t he otherwise desirable use of radical cycliza-tions and cyclization cascades to assemble such systems is rare.…”