Gong-Qing Liu

Intramolecular Aminoboration of Unfunctionalized Olefins

A direct and catalyst-free method for the intramolecular aminoboration of unfunctionalized olefins is reported. In the presence of BCl3 (1 equiv) as the sole boron source, intramolecular aminoboration of sulfonamide derivatives of 4-penten-1-amines, 5-hexen-1-amines, and 2-allylanilines proceeded readily without the use of any catalyst. The boronic acids obtained after hydrolysis could be converted into the corresponding pinacol borates in a straightforward manner by treatment with pinacol under anhydrous conditions.

Preparation of trans-2-Substituted-4-halopiperidines and cis-2-Substituted-4-halotetrahydropyrans via AlCl3-Catalyzed Prins Reaction

A general and practical method for the preparation of trans-2-substituted-4-halopiperidines and cis-2-substituted-4-halotetrahydropyrans is reported. Using 5 mol % of AlCl3 as the catalyst and 2 equiv of trimethylsilyl halides as the halide sources, aza-Prins cyclization of N-tosyl homoallylamine or Prins cyclization of homoallylic alcohol with carbonyl compounds could be readily realized, giving the corresponding trans-2-substituted-4-halopiperidines or cis-2-substituted-4-halotetrahydropyrans in high yields and satisfactory diastereoselectivity.

Cooperative effect in organocatalytic intramolecular hydroamination of unfunctionalized olefins

The cooperative effect in organocatalytic hydroamination of unfunctionalized olefins was reported. In the presence of 3-hydroxy-2-naphthoic acid, N-benzyl 4-penten-1-amines and 5-hexen-1-amines produced the intramolecular cyclization products in good isolated yields.

mCPBA-mediated metal-free intramolecular aminohydroxylation and dioxygenation of unfunctionalized olefins

mCPBA-mediated metal-free intramolecular aminohydroxylation and dioxygenation reactions of unfunctionalized olefins are reported. In the presence of 1.2 equiv. of m-chlorobenzoic peracid, different N-sulfonyl 4-penten-1-amine substrates could be cyclized via epoxide intermediates, producing the corresponding 2-hydroxymethylpyrrolidine products in up to 92% yields. The reaction could be carried out at gram-scale, and the hydroxyl group could be further converted to a variety of different functional groups via conventional functional group transformation reactions. When N-sulfonyl carboxylimides were subjected to the same reaction, O-cyclization products oxolanimines were obtained. The skeletons of these compounds were confirmed using X-ray diffraction experiments.

Transition metal-free iodine-promoted haloamination of unfunctionalized olefins

A transition metal-free route to 3-halopiperidines and 2-halomethylpiperidines was described. In the presence of iodine, potassium persulfate and a suitable halogen source, intramolecular haloamination of 4-penten-1-amines and 5-hexen-1-amines proceeded readily, leading to the corresponding substituted piperidines in good isolated yields.

On the understanding of BF3·Et2O-promoted intra- and intermolecular amination and oxygenation of unfunctionalized olefins

BF3·Et2O was found to be effective for both intra- and intermolecular amination and oxygenation of unfunctionalized olefins. In the presence of 3 equiv. of BF3·Et2O, intramolecular hydroamination of N-(pent-4-enyl)-p-toluenesulfonamides, N-(hex-5-enyl)-p-toluenesulfonamides, intermolecular hydroamination between sulfonamides and cyclohexene, norbornene or styrene, lactonization of pent-4-enoic acid or hex-5-enoic acid compounds and esterification of cyclohexene with different carboxylic acids all proceeded readily, leading to the corresponding amination or oxygenation products in up to 99% isolated yields. Preliminary NMR experiments and DFT calculations suggested that the intramolecular hydroamination reactions proceeded via a sulfonimidic acid intermediate (NS–OH), and formation of the corresponding Bronsted acid HF or HBF4 was less likely.