No abstract

Benzynes were generated from o-(trimethylsilyl)phenols using nonafluorobutanesulfonyl fluoride (NfF) by a domino process, i.e., the nonaflation of the phenolic hydroxyl group of o-(trimethylsilyl)phenols by NfF followed by the attack of the produced fluoride ion on the trimethylsilyl group. The generated benzyne immediately underwent various reactions to give polysubstituted benzenes.

Cause and effect: The first ortho‐selective nucleophilic addition reaction of amines to 3‐substituted benzynes has been achieved. Despite a large trimethylsilyl substituent, primary amines attack the C2 position of 3‐silylbenzynes to produce 2‐silylanilines (see scheme). This outcome is likely to result from the inductive electron‐donating effect of the silyl group, which overrides its steric repulsion with the approaching amines.

Nucleophilic addition of amines to 3-[(dan)boryl]benzynes (dan = 1,8-diaminonaphthalene) generated by a fluoride ion proceeded with high ortho-selectivity to give 2-borylaniline derivatives, under conditions that are tolerant to various functional groups. The (dan)boryl group of the adduct was hydrolyzed into a boronic acid under acidic conditions, which could further serve for various C-C, C-O, C-N, and C-H bond-formation reactions. The overall process provides a promising entry for preparing multisubstituted aniline derivatives.

Benzo-fused nitrogen-containing heterocycles are abundant in biologically active compounds. One of the most important methods for preparing such heterocycles is the (3 + 2) cycloaddition reaction of benzynes with 1,3-dipolar compounds. However, the reactions of unsymmetrically substituted benzynes generally show low selectivity and hence yield mixtures of two regioisomers. In this paper, we describe the synthesis of both regioisomers of multisubstituted benzo-fused azole derivatives such as benzotriazoles, 1H-indazoles, and benzo[d]isoxazoles through the regiocomplementary (3 + 2) cycloaddition reactions of 3-boryl- and 3-silylbenzynes with 1,3-dipoles. The improved generation of 3-borylbenzynes from new precursors was one of the most important results of this work, which produced the successful (3 + 2) cycloaddition reactions with exclusive and proximal selectivities. On the other hand, similar reactions of 3-silylbenzynes selectively afforded distal cycloadducts. Analysis of the reaction pathways of these amazing regioselectivities by density functional theory calculations revealed that the (3 + 2) cycloadditions of borylbenzynes are controlled by the electrostatic effect of the boryl group, while those of silylbenzynes are controlled mainly by the steric effect of the bulky silyl groups that produced electrostatically unfavorable adducts via anomalous transition states.