Triflic Anhydride (Tf2O)-Activated Transformation of Amides, Sulfoxides and Phosphorus Oxides via Nucleophilic Trapping

Trifluoromethanesulfonic anhydride (Tf2O) has found a wide range of applications in synthetic organic chemistry as a strong electrophilic activator leading to the transient generation of a triflate intermediate. This versatile triflate intermediate undergoes nucleophilic trapping with diverse nucleophiles to yield novel compounds. In this review, we describe the features and applications of triflic anhydride in organic synthesis reported in the past decade, especially in amide, sulfoxide, and phosphorus oxide chemistry through electrophilic activation. A plausible mechanistic pathway of each important reaction is also discussed.

A General Approach to 2,2-Disubstituted Indoxyls: Total Synthesis of Brevianamide A and Trigonoliimine C

The indoxyl unit is a common structural motif in alkaloid natural products and bioactive compounds. Here, we report a general method that transforms readily available 2-substituted indoles into 2,2-disubstituted indoxyls via nucleophile coupling with a 2-alkoxyindoxyl intermediate and showcase its utility in short total syntheses of the alkaloids brevianamide A (7 steps) and trigonoliimine C (6 steps). The developed method is operationally simple and demonstrates broad scope in terms of nucleophile identity and indole substitution, tolerating 2-alkyl substituents and free indole N–H groups, elements beyond the scope of most prior approaches. Spirocyclic indoxyl products are also accessible via intramolecular nucleophilic trapping.

A General Approach to 2,2-Disubstituted Indoxyls: Total Synthesis of Brevianamide A and Trigonoliimine C

The indoxyl unit is a common structural motif in alkaloid natural products and bioactive compounds. Here, we report a general method that transforms readily available 2-substituted indoles into 2,2-disubstituted indoxyls via nucleophile coupling with a 2-alkoxyindoxyl intermediate and showcase its utility in short total syntheses of the alkaloids brevianamide A (7 steps) and trigonoliimine C (6 steps). The developed method is operationally simple and demonstrates broad scope in terms of nucleophile identity and indole substitution, tolerating 2-alkyl substituents and free indole N–H groups, elements beyond the scope of most prior approaches. Spirocyclic indoxyl products are also accessible via intramolecular nucleophilic trapping.

Synthesis of Fused Oxepane HIV Integrase Inhibitor MK-1376

Controlling the absolute and relative stereochemistry of a seven-membered oxepane in the formation of HIV integrase inhibitor MK-1376 was accomplished through a strategy involving the use of asymmetric allylation and stereoconvergent, substrate-directed installation of an amine fragment. Surprising reactivity was demonstrated during the asymmetric allylation in which the allyl-pyrimidone product was formed reversibly. The stereoconvergent amine addition was accomplished through an elimination/addition sequence involving a quinone methide reactive intermediate, and nucleophilic trapping of the reactive quinone methide intermediate with methylamine. This novel approach delivered MK-1376, offering 100-fold greater productivity and 50-fold less waste than the initial synthetic chemistry route.

Rearrangement and nucleophilic trapping of bicyclo[4.1.0]hept-2-yl derived nonclassical bicyclobutenium ions

Here we describe the synthesis of two specifically labelled 13C isotopologues of cis-2-(4-nitrophenoxy)bicyclo[4.1.0]heptane and their solvolysis reactions in trifluoroethanol. By using one- and two-dimensional 1H- and 13C-NMR spectroscopy, we characterized the pathways for the rearrangement of these isotopologues to give 13C-labelled 4-(2,2,2-trifluoroethoxy)cycloheptene. We show that the initially formed cationic intermediate undergoes a degenerate rearrangement, which does not reach equilibrium before nucleophilic capture of the cation. Moreover, we show that the nonclassical carbocation, cyclohept-3-ene(3,1,4-deloc)ylium, gives an approximate 6:1 ratio of the cis- to trans-diastereomeric 2-(2,2,2-trifluoroethoxy)bicyclo[4.1.0]heptane as reaction intermediates that subsequently solvolyze to the 4-(2,2,2-trifluoroethoxy)cycloheptene product.

One-pot functionalisation of N-substituted tetrahydroisoquinolines by photooxidation and tunable organometallic trapping of iminium intermediates

Nucleophilic trapping of iminium salts generated via oxidative functionalisation of tertiary amines is well established with stabilised carbon nucleophiles. The few reports of organometallic additions have limited scope of substrate and organometallic nucleophile. We report a novel, one-pot methodology that functionalises N-substituted tetrahydroisoquinolines by visible light-assisted photooxidation, followed by trapping of the resultant iminium ions with organometallic nucleophiles. This affords 1,2-disubstituted tetrahydroisoquinolines in moderate to excellent yields.