A redox-neutral, mild, and simple protocol is developed for the synthesis of functionalized phenols from para-quinone methides upon visible-light irradiation.

Benzylic and allylic halides were conveniently oxidized to aldehydes and ketones by pyridine Noxide in the presence of silver oxide under mild conditions. Aldehydes and ketones, especially aromatic and α,β-unsaturated carbonyl compounds, are important classes of chemicals. Methods for direct conversion of halides to carbonyl compounds have been reviewed. 1,2 Dimethyl sulfoxide (DMSO) is often employed as the oxygen donor. 3,4 However, high temperature is usually required. 3,4 Oxidations involving amine oxides have also been reported. [5][6][7] In our attempt to modify carbohydrates with benzylic halides, we have found that pyridine N-oxide can effectively and conveniently oxidize benzylic and allylic halides to aromatic and α,β-unsaturated carbonyl compounds, respectively, in the presence of silver oxide (Ag 2 O) under mild conditions. 8,9The reactions were carried out in acetonitrile (toluene and tetrahydrofuran gave much lower yield). The reaction mechanism should be identical to that proposed for the reaction with DMSO and base, as shown in Scheme 1. 1,8 Half equivalent of silver oxide was utilized to facilitate the reaction. Silver oxide assists the heterolysis of the carbon-halogen bond in the substitution reaction with pyridine N-oxide. The resulting hydroxide ion from the reaction between silver oxide and halogen then functions as the base in the elimination reaction to produce the carbonyl group. When DMSO was employed instead of pyridine N-oxide as the source of oxygen, the reaction did not go to completion while giving a mixture of products.For most bromides, the reactions were conveniently carried out at room temperature. The reaction was complete in a few hours but was stirred overnight for convenience. For chlorides and some benzyl bromides with very strong electron-withdrawing substituents, slightly elevated temperature (50 °C) was required (Entries 4-7 and 12-15 in Table 1). For some chlorides, only partial conversion was observed (Entries 13 and 14). The substituent effects indicate a S N 1-like mechanism for the first step in the reaction pathway.The reaction workup was very simple. Upon completion of the reaction, sodium sulfate or magnesium sulfate was added and the resulting mixture was filtered through a thin layer of Celite. Concentration of the filtrate gave essentially pure product in quantitative yield. 10

An iron(iii)-controlled selective N–O bond cleavage was developed for the synthesis of tetrasubstituted pyridines and isoxazolines from N-vinyl-α,β-unsaturated ketonitrones.

A simple and mild protocol is developed for the synthesis of β-trifluoromethyl alcohols from alkenes.

A novel photocatalytic protocol is herein described for the preparation of functionalized phenols via radical alkylation of para-quinone methides under transition-metal-free conditions. The reaction is external oxidant free and performed at ambient temperature upon visible light irradiation, allowing the access to various desired products in satisfactory yields. The readily available 4-alkyl-1,4-dihydropyridines serve as the effective alkyl radical precursors.

A 2,2,6,6-tetramethyl- N-oxopiperidinium (TEMPO)-mediated three-component diverse transformation of vinyl azides under metal-free conditions is described. The reaction protocols are operationally simple and conducted at ambient temperature, allowing to access various TEMPO-trapped ketones, amides, and α-alkoxyalkyl azides. Preliminary mechanistic studies indicate that an alkene radical cation-mediated radical-radical cross-coupling C-O bond formation could be involved.

A copper-catalyzed atom economical O-transfer reaction strategy was developed for the synthesis of densely functionalized γ-lactones from N-vinyl-α,β-unsaturated nitrones and ketenes.

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 BF 3 -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.