Chemoselective Synthesis of 1,1-Disubstituted Vinyl Triflates from Terminal Alkynes Using TfOH in the Presence of TMSN3.

1,1-Disubstituted vinyl triflates are synthesized by direct hydrotriflation of terminal alkynes employing a combination of TfOH and TMSN3 in DCM at room temperature. Interestingly, under these conditions, only terminal alkynes were selectively converted to the corresponding vinyl triflates, while internal alkynes were not reacted. A broad range of substrates were successfully converted to the corresponding 1,1-disubstituted vinyl triflates in good to excellent yields even those with internal alkyne moieties present in the molecules.

Construction of 5-Aminotetrazoles via in Situ Generation of Carbodiimidium Ions from Ketones Promoted by TMSN3/TfOH.

A novel synthetic approach for the synthesis of 5-aminotetrazoles has been developed by employing simple ketones as substrates. This methodology involved the N2-extrusion/aryl migration of azido complexes as the key step for the in situ generation of carbodiimidium ion, which could further react with hydrazoic acid and cyclize intramolecularly to provide 5-aminotetrazoles in good to excellent yields. In addition, the regioselectivity of the reaction was studied and rationalized by density functional theory calculations.

Silver-Catalyzed Cyclization of ortho-Carbonylarylacetylenols for the Synthesis of Dihydronaphthofurans.

ortho-Carbonylarylacetylenols have been employed for the synthesis of dihydronaphthofurans via AgTFA-catalyzed annulation reaction. A broad range of substrates both ortho-keto- and ortho-formylarylacetylenols could be employed in this transformation providing the desired products in good yields. However, the reaction pathways of these two substrates are different. The reaction of the ketone precursors could directly lead to the desired products in a single operation while the reaction of the aldehyde precursors required a one-pot two-step approach, without isolation of the bicyclic acetal intermediates. In addition, this method was also successfully used for the synthesis of dihydronaphthopyrans in very good yields.

Utility of Nitrogen Extrusion of Azido Complexes for the Synthesis of Nitriles, Benzoxazoles, and Benzisoxazoles.

The utility of the nitrogen extrusion reaction of azido complexes, generated in situ from the corresponding aldehydes or ketones with TMSN3 in the presence of ZrCl4 or TfOH, has been described. These azido complexes could undergo three different pathways, depending on the substrates. First, azido methanolate complexes or imine diazonium ions could lead to benzisoxazole products via an intramolecular nucleophilic substitution. Second, imine diazonium ions could also undergo either the elimination of proton to provide nitrile products in good to excellent yields or an aryl migration, followed by an intramolecular nucleophilic addition, to give benzoxazole products in good yields.

Regioselective Synthesis of 3-Bromoquinoline Derivatives and Diastereoselective Synthesis of Tetrahydroquinolines via Acid-Promoted Rearrangement of Arylmethyl Azides.

Regioselective synthesis of 3-bromoquinoline derivatives was achieved via a formal [4 + 2]-cycloaddition between N-aryliminium ion, generated from arylmethyl azides, and 1-bromoalkynes. This method could also be applied to other quinoline derivatives using appropriate alkynes. Moreover, the current strategy could be utilized for the diastereoselective synthesis of tetrahydroquinoline derivatives employing alkenyl substrates in good to excellent yields.