A highly diastereoselective [3+3] annulation reaction of aza-oxyallyl cations and nitrones

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

1,3-Dipolar cycloaddition of nitrones: synthesis of multisubstituted, diverse range of heterocyclic compounds

The 1,3-dipolar cycloaddition reaction of nitrone is one of the most important methods for the synthesis of different sizes of heterocycles which have enormous applications in natural products, biologically active molecules and pharmaceuticals.

Synthesis of α-aminooxy amides through [3 + 3] cycloaddition and Sc(OTf)3-catalyzed double C-N bond cleavage in a one-pot reaction

Various α-aminooxy amides bearing a quaternary carbon at the α-position were prepared in good to excellent yields under mild reaction conditions from N-vinyl nitrones and α-bromohydroxamates. The N-vinyl nitrones tolerate a wide range of N-vinyl fluorenone nitrones and N-vinyl isatin nitrones. Mechanistic studies show that the reaction initially proceeds through [3 + 3] cycloaddition between N-vinyl nitrones and aza-oxyallyl cations generated from α-bromohydroxamates to afford six-membered N,O-heterocycles, followed by double C-N bond cleavage in the presence of the Sc(OTf)3 catalyst. A selective N-O bond cleavage of the obtained α-aminooxy amides is also realized under Fe/NH4Cl conditions. Furthermore, gram-scalable preparations of α-aminooxy amides are easily achieved.

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C-N, C-O and C-S bond forming reactions, and later widely employed in C-C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.

An efficient synthesis of oxazolines via a cascade reaction between azaoxyallyl cations and 1,2-benzisoxazoles

A formal [3 + 2] cycloaddition reaction between the C and O terminals of azaoxyallyl cations formed in situ and 1,2-benzisoxazoles has been realized. This one-pot cycloaddition method provided an effective and practical pathway to synthesize oxazoline in good yields under mild conditions. The title products exhibited unique fluorescence properties.

Amant C, Sun S, Xing Y. Synthesis of 1,2,4-oxadiazolidines via [3+2] cycloaddition of nitrones with carbodiimides

An efficient [3+2] cycloaddition of nitrones and carbodiimides has been developed.

α-Halogenoacetamides: versatile and efficient tools for the synthesis of complex aza-heterocycles

This review presents the use of α-alkyl- and α-alkoxy-halogenoacetamides as powerful partners for domino and 1,3-dipolar cycloaddition reactions resulting in a ring closure.

Synthesis of 1,2-Oxazinanes via Hydrogen Bond Mediated [3 + 3] Cycloaddition Reactions of Oxyallyl Cations with Nitrones

Reported herein is the development of [3 + 3] cycloaddition reactions between oxyallyl cations and nitrones to yield 1,2-oxazinane heterocycles. Oxyallyl cation intermediates, generated in situ from α-tosyloxy ketones in the presence of hexafluoro-2-propanol (HFIP), a cosolvent, and a base, are found to react with a range of nitrones to afford 1,2-oxazinanes in good to high yields. The reactions are catalyzed by hydrogen-bond donors such as phenols and squaramides, and dramatically higher diastereoselectivities are observed with 4-nitrophenol.