Synthesis of N-(2-Hydroxyaryl)benzotriazoles via Metal-Free O-Arylation and N–O Bond Cleavage

Cycloadditions of Benzynes with the Azoxy [RN═N+(O-)R'] 1,3-Dipole Tautomer of 1-Hydroxybenzotriazole (HOBT)

1,3-Dipolar cycloadditions of azoxy species are rare. HOBT exists as a pair of tautomers, one of which contains an azoxy subunit. We show that heavily substituted, thermally generated benzynes react with HOBT by engaging the azoxy tautomer to give products having a benzotriazole with a benzyne-derived o-hydroxyaryl group at N2. DFT calculations were used to probe aspects of the mechanism. HOBT analogs of the uronium family (HBTU, HCTU, TATU, and HATU) react in an analogous fashion. The parent 1,2-dehydrobenzene (o-benzyne) generated by the action of (basic) CsF reacts with HOBT in an orthogonal manner to give, exclusively, an N1-arylated product.

Rh(II)-catalysed N2-selective arylation of benzotriazoles and indazoles using quinoid carbenes via 1,5-H shift

An efficient Rh(II)-catalyzed highly selective N2-arylation of benzotriazole, indazole, and 1,2,3 triazole is developed using diazonaphthoquinone. The developed protocol is extended with a wide scope. In addition, late-stage arylation of these scaffolds tethered with bioactive molecules is explored. Control experiments and DFT calculations reveal that the reaction proceeds presumably via nucleophilic addition of the N2 (of the 1H tautomer) center to quinoid-carbene followed by a 1,5-H shift.

1-Benzyloxy-5-phenyltetrazole derivatives highly active against androgen receptor-dependent prostate cancer cells

A series of 1-benzyloxy-5-phenyltetrazole derivatives and similar compounds were synthesized and evaluated for their in vitro inhibitory activity against androgen-receptor-dependent (22Rv1) and androgen-receptor independent (PC3) prostate cancer cells. The most active compounds had in vitro IC₅₀ values against 22Rv1 cells of <50 nM and showed apparent selectivity for this cell type over PC3 cells; however, these active compounds had short half-lives when incubated with mouse liver microsomes and/or when plasma concentration was monitored during in vivo pharmacokinetic studies in mice or rats. Importantly, lead compound 1 exhibited promising inhibitory effects on cell proliferation, expression of AR and its splicing variant AR-v7 as well as AR regulated target genes in 22Rv1 cells, which are so called castration-resistant prostate cancer (CRPC) cells, and a 22Rv1 CRPC xenograft tumour model in mice. Structural changes which omitted the N-O-benzyl moiety led to dramatic or total loss of activity and S-benzylation of a cysteine derivative, as a surrogate for in vivo S-nucleophiles, by representative highly active compounds, suggested a possible chemical reactivity basis for this "activity cliff" and poor pharmacokinetic profile. However, representative highly active compounds did not inhibit a cysteine protease, indicating that the mode of activity is unlikely to be protein modification by S-benzylation. Despite our efforts to elucidate the mode of action, the mechanism remains unclear.

Chan-Lam Reaction and Lewis Acid Promoted 1,3-Rearrangement of N-O Bonds to Prepare N-(2-Hydroxyaryl)pyridin-2-ones

We describe the difunctionalization of arylboronic acids to prepare various N-(2-hydroxyaryl)pyridin-2-ones in good yields using N-hydroxypyridin-2-ones as the oxygen and nitrogen sources through a copper(II)-catalyzed Chan-Lam reaction and subsequent BF₃-promoted selective 1,3-rearrangement of N-O bond in a one-pot procedure. Mechanistic studies reveal that the 1,3-rearrangement selectivity is controlled by the formation of the key aryloxypyridinium salt. The obtained products are easily converted to various useful pyridin-2-one scaffolds.

Diaryliodonium(III) Salts in One-Pot Double Functionalization of C–IIII and ortho C–H Bonds

Since the 1950s, diaryliodonium(III) salts have been demonstrated to participate in various arylation reactions, forming aryl–heteroatom and aryl–carbon bonds. Incorporating the arylation step into sequential transformations would provide access to...

The Disappearing Director: The Case of Directed N-Arylation via a Removable Hydroxyl Group

A facile and broadly applicable method for the regiospecific N-arylation of benzotriazoles is reported. Copper-mediated reactions of diverse 1-hydroxy-1H-benzotriazoles with aryl boronic acids lead to 1-aryl-1H-benzotriazole 3-oxides. A N1-OH → N3 prototropy in the 1-hydroxy-1H-benzotriazoles is plausibly the underlying basis, where the tautomer is captured by the boronic acid, leading to C-N (not C-O) bond formation. Because the N-O bond in amine N-oxides and 1-hydroxy-1H-benzotriazoles can be easily reduced by diboron reagents such as (pinB)2 and B2(OH)4, exposure of the 1-aryl-1H-benzotriazole 3-oxides to B2(OH)4 then leads to facile reduction of the N-O bond resulting in diverse, regiospecifically-arylated benzotriazoles. Thus, the N-hydroxyl group in 1-hydroxy-1H-benzotriazoles acts as a disposable arylation director.

Enantiospecific sp2 -sp3 Coupling of ortho- and para-Phenols with Secondary and Tertiary Boronic Esters

The coupling of ortho- and para-phenols with secondary and tertiary boronic esters has been explored. In the case of para-substituted phenols, after reaction of a dilithio phenolate species with a boronic ester, treatment with Ph3 BiF2 or Martin's sulfurane gave the coupled product with complete enantiospecificity. The methodology was applied to the synthesis of the broad spectrum antibacterial natural product (-)-4-(1,5-dimethylhex-4-enyl)-2-methyl phenol. For ortho-substituted phenols, initial incorporation of a benzotriazole on the phenol oxygen atom was required. Subsequent ortho-lithiation and borylation gave the coupled product, again with complete stereospecificity.