Rhodium(II)‐Catalyzed Formal [4+1]‐Cycloaddition of Pyridotriazoles and Propargyl Alcohols: Synthesis of 2,5‐Dihydrofurans

Abstract

A rhodium-catalyzed formal [4 + 1]-cycloaddition of pyridotriazoles and aryl propargyl alcohols is reported, providing an effective access to 2-pyridyl-substituted 2,5-dihydrofuran derivatives in moderate to high yields. Mechanistically, the proposed oxonium ylide intermediate in this catalytic alkyne carbocyclization transformation is verified by an interception experiment for the first time.

Asymmetric Three-Component Propargyloxylation for Direct Assembly of Polyfunctionalized Chiral Succinate Derivatives

“…For other pyridotriazole derivatives, such as nonsubstituted, 4-methyl, and 6-Br, higher temperature is essential to initiate the reaction (115-140°C). 60 Thus, byproducts generated via [3+2] cyclization of the corresponding ylide intermediate, 58 instead of interception by imine, were formed as the major products in these cases. The 7-methyl pyridotriazole showed no reactivity at −10°C, and slow decomposition was observed when the reaction was warmed to 60°C; whereas, the 7-trifluoromethyl pyridotriazole is reactive under the current conditions.…”

“…The 1,2-H shift, cyclization, and [2,3]-sigmatropic rearrangement (when R = alkyne) reactions could then occur to produce the corresponding byproducts through this ylide species. [57][58][59] Interception of this active intermediate with electrophilic imines in the presence of CPA 5e could successfully deliver the three-component products 4 and regenerate the catalysts. The observed stereochemistry in this reaction is depicted by the interaction model reported by Simon and Goodman, [65][66][67][68][69] which has been used to explain the stereochemical outcome of analogous Mannich-type addition in the presence of CPA via the dual H-bonding model.…”

“…To be successful, our hypothesis must address significant limitations. First, the potential side reactions, including the direct cyclopropenation reaction with alkyne species, 55,56 and others (Scheme 1e, in the dashed frame), [57][58][59] might occur, which is one of the main challenges needing to be addressed. The second challenge is enantioselective control during the formation of a quaternary carbon center.…”

Rhodium‐Catalyzed O−H Bond Insertion Reaction between H‐Phosphoryl Compounds and 2‐Pyridyl Carbenes Generated from Pyridotriazoles

“…In the presence of the rhodium catalyst, [23] pyridotriazole 1 may decompose to form the transient Rh‐carbene intermediate A with the loss of one molecule of nitrogen. The nucleophilic attack of the oxygen atom of the tautermized phosphinous acid R 2 POH may take place to produce the rhodium intermediate C [24] . A stepwise process of ligand exchange with R 2 POH at the rhodium center to produce a coordinate intermediate B followed by an intramolecular oxo‐nucleophilic attack to the carbon center may also be possible to generate the intermediate C .…”

Recent Advances in Denitrogenative Reactions of Pyridotriazoles

“…A rhodium(II)-catalyzed denitrogenative reaction of pyridotriazoles 22 with aryl propargyl alcohols 23 yielding 2,5-dihydrofuran derivatives 24 has been reported by Xu, Hu and co-workers (Scheme 6). 13 Various propargyl alcohols 23, especially those with electron-withdrawing groups, gave high yields of the products 24. The reaction was sensitive to the steric effect of an ortho substituent on the alcohol 23.…”