The use of vinyl
electrophiles in synthesis has been hampered by
the lack of access to a suitable reagent
that is practical and of appropriate reactivity. In this work we introduce
a vinyl thianthrenium salt as an effective vinylating reagent. The
bench-stable, crystalline reagent can be readily prepared from ethylene
gas at atmospheric pressure in one step and is broadly useful in the
annulation chemistry of (hetero)cycles, N-vinylation of heterocyclic
compounds, and palladium-catalyzed cross-coupling reactions. The structural
features of the thianthrene core enable a distinct synthesis and reactivity
profile, unprecedented for other vinyl sulfonium derivatives.
Synthesis of bicyclic scaffolds has attracted tremendous attention because they are playing an important role as saturated bioisosteres of benzenoids in modern drug discovery. Here, we report a BF3‐catalyzed [2π+2σ] cycloaddition of aldehydes with bicyclo[1.1.0]butanes (BCBs) to access polysubstituted 2‐oxabicyclo[2.1.1]hexanes. A new kind of BCB containing an acyl pyrazole group was invented, which not only significantly facilitates the reactions, but can also serve as a handle for diverse downstream transformations. Furthermore, aryl and vinyl epoxides can also be utilized as substrates which undergo cycloaddition with BCBs after in situ rearrangement to aldehydes. We anticipate that our results will promote access to challenging sp3‐rich bicyclic frameworks and the exploration of BCB‐based cycloaddition chemistry.
Radical addition reactions of olefins have emerged as an attractive tool for the rapid assembly of complex structures, and have plentiful applications in organic synthesis, however, such reactions are often limited to polymerization or 1,2-difunctionalization. Herein, we disclose an unprecedented radical relay 1,4oxyimination of two electronically differentiated olefins with a class of bifunctional oxime carbonate reagents via an energy transfer strategy. The protocol is highly chemo-and regioselective, and three different chemical bonds (C−O, C−C, and C−N bonds) were formed in a single operation in an orchestrated manner. Notably, this reaction provides rapid access to a large variety of structurally diverse 1,4-oxyimination products, and the obtained products could be easily converted into valuable biologically relevant δ-hydroxyl-α-amino acids. With a combination of experimental and theoretical methods, the mechanism for this 1,4-oxyimination reaction has been investigated. Theoretical calculations reveal that a radical chain mechanism might operate in the reaction.
Cycloaddition reactionsepitomized by the Diels–Alder
reactionoffer an arguably unmatched springboard for achieving
chemical complexity, often with excellent selectivity, in a modular
single step. We report the synthesis of aza-acenaphthenes in a single
step by an unprecedented formal peri-(3 + 2) cycloaddition
of simple quinolines with alkynes. A commercially available iridium
complex exerts a dual role of photosensitizer and photoredox catalyst,
fostering a cyclization/rearomatization cascade. The initial energy-transfer
phase leads to the acenaphthene skeleton, while the ensuing redox
shuttling step leads to aromatization. We applied this technology
to 8-substituted quinolines and phenanthrolines, which smoothly reacted
with both terminal and internal alkynes with excellent levels of regio-
and diastereoselectivity. Density functional theory calculations revealed
the intertwined EnT/SET nature of the process and offered guiding
design principles for the synthesis of new aza-acenaphthenes.
Intermolecular carboamination of olefins offers a powerful platform for the rapid construction of structurally complex amines from abundant feedstocks. However, these reactions often require transition-metal catalysis, and are mainly limited...
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