Total Synthesis of Alanense A through an Intramolecular Friedel-Crafts Alkylation

The first total synthesis of cadinane sesquiterpenoid alanense A, in which an intramolecular dehydrative Friedel-Crafts alkylation of 2,5-diaryl-2-pentanol is incorporated as a key step, has been achieved. The combinatorial use of p-TsOH·H2O as a catalyst and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a solvent provides 1,1-disubstituted tetrahydronaphthalene in 97% yield. It was also found that the combination of p-TsOH and HFIP is effective for the removal of phenolic MOM ether.

Metal-Free Construction of Multisubstituted Indolizines via Intramolecular Amination of Allylic Alcohols

An intramolecular amination of allylic alcohols is developed as an efficient and general access to biologically important multisubstituted indolizines and their variants. Two metal-free synthetic platforms including using aqueous hydrochloric acid solution as the solvent and p-toluenesulfonic acid as the catalyst have been established, enabling the divergent synthesis of these valuable compounds in high yields.

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.

Oxyallyl cation promoted dearomative semipinacol rearrangement: a facile stereodivergent synthesis of spiro-indolines with contiguous quaternary centers

A novel oxyallyl cation promoted semipinacol rearrangement of indole-type allylic alcohols was disclosed for the stereodivergent synthesis of spiro-indolines. A variety of spiro-indolines were obtained with moderate to good yields. Three contiguous stereocenters, two of which are vicinal quaternary centers, were effectively formed with good diastereoselectivity. It is worth noting that two diastereoisomers of rearranged products can be readily achieved by easily regulating the reaction conditions. This method may provide an applicable approach for the synthesis of natural indole alkaloids.

Formal Enone α-Arylation via I(III)-Mediated Aryl Migration/Elimination

A formal enone α-arylation is described. This metal-free transformation relies on the I(III)-mediated skeletal reorganization of silyl enol ethers and features mild conditions, good yields, and high stereoselectivities for β-substituted enones.

Access to Vinyl Ethers and Ketones with Hypervalent Iodine Reagents as Oxy-Allyl Cation Synthetic Equivalents

We report an Umpolung strategy of enol ethers to generate oxy-allyl cation equivalents based on the use of hypervalent iodine reagents. Under mild basic conditions, the addition of nucleophiles to aryloxy-substituted vinylbenziodoxolone (VBX) reagents, easily available in two steps from silyl alkynes, resulted in the stereoselective formation of substituted aryl enol ethers. The reaction was most efficient with phenols as nucleophiles, but preliminary results were also achieved for C- and N- nucleophiles. In absence of external nucleophiles, the 2-iodobenzoate group of the reagent was transferred. The obtained aryl enol ethers could then be transformed into α-difunctionalized ketones by oxidation. The described "allyl cation"-like reactivity contrast with the well-established "vinyl-cation" behavior of alkenyl iodonium salts.

Transition metal-free synthesis of α-aryl ketones via oxyallyl cation capture with arylboronic acids

α-Arylated ketones were accessed via oxyallyl cation capture with arylboronic acids in good yields with broad substrate tolerance.