Selective Alkynylallylation of the C-C σ Bond of Cyclopropenes

Selective Cleavage of α-Olefins to Produce Acetylene and Hydrogen

Acetylene production from mixed α-olefins emerges as a potentially green and energy-efficient approach with significant scientific value in the selective cleavage of C-C bonds. On the Pd(100) surface, it is experimentally revealed that C2 to C4 α-olefins undergo selective thermal cleavage to form surface acetylene and hydrogen. The high selectivity toward acetylene is attributed to the 4-fold hollow sites which are adept at severing the terminal double bonds in α-olefins to produce acetylene. A challenge arises, however, because acetylene tends to stay at the Pd(100) surface. By using the surface alloying methodology with alien Au, the surface Pd d-band center has been successfully shifted away from the Fermi level to release surface-generated acetylene from α-olefins as a gaseous product. Our study actually provides a technological strategy to economically produce acetylene and hydrogen from α-olefins.

Iron(II) Phthalocyanine-Catalyzed Olefination of Aldehydes with Diazoacetonitrile: A Novel Approach to Construct Alkenyl Nitriles

A novel synthetic approach to preparing alkenyl nitriles via the olefination of aldehydes with diazoacetonitrile catalyzed by iron(II) phthalocyanine in the presence of PPh3 has been developed. A broad variety of aldehydes are efficiently transformed into the corresponding products with the high yields of 75%-97%. And it is also suitable for its gram-scale preparation. The suggested mechanism involves the transformation of the phosphazine to ylide by iron(II) phthalocyanine.

Bidirectional Iterative Approach to Sequence-Defined Unsaturated Oligoesters

Herein, we describe the development of a new strategy for the synthesis of unsaturated oligoesters via sequential metal- and reagent-free insertion of vinyl sulfoxonium ylides into the O-H bond of carboxylic acid. Like two directional coupling of amino acids (N- to C-terminal and C- to N-terminal) in peptide synthesis, the present approach offers a strategy in both directions to synthesize oligoesters. The sequential addition of the vinyl sulfoxonium ylide to the carboxylic acids (acid iteration sequence) in one direction and the sequential addition of the carboxylic acids to the vinyl sulfoxonium ylide (ylide iteration sequence) in another direction yield (Z)-configured unsaturated oligoesters. To perform this iteration, we have developed a highly regioselective insertion of vinyl sulfoxonium ylide into the X-H (X = O, N, C, S, halogen) bond of acids, thiols, phenols, amines, indoles, and halogen acids under metal-free reaction conditions. The insertion reaction is applied to a broad range of substrates (>50 examples, up to 99% yield) and eight iterative sequences. Mechanistic studies suggest that the rate-limiting step depends on the type of X-H insertion.

Fe-Catalyzed Selective Formal Insertion of Diazo Compounds into C(sp)-C(sp3) Bonds of Propargyl Alcohols: Access to Alkyne-Substituted All-Carbon Quaternary Centers

The construction of all-carbon quaternary centers, especially those containing an alkyne-substituted framework, represents an important challenge in organic synthesis. Here we present a novel Fe-catalyzed selective formal insertion of diazo compounds into C(sp)-C(sp³) bonds of propargyl alcohols under mild conditions that enables the streamlined construction of alkyne-substituted all-carbon quaternary centers. This unique strategy starts with in situ generation of an ester group in the presence of carboxylic acids, followed by insertion of metal-carbene into C(sp)-C(sp³) bonds, which may open up a new reaction mode for exploring metal-carbene insertion into acyclic C-C bonds.

Visible-Light-Induced Organocatalyzed [2+1] Cyclization of Alkynes and Trifluoroacetylsilanes

The synthesis of common cyclopropenes has been widely studied, but the synthesis of cyclopropenols is a significant challenge. Herein, we highlight our recent work on the synthesis of trifluoromethylated cyclopropenols through [2+1] cycloaddition reaction between alkynes and trifluoroacetylsilanes under visible-light-induced organocatalysis. The novel amphiphilic donor-acceptor carbenes derived from trifluoroacetylsilanes can react effectively with both activated and unactivated alkynes. Broad substrate scope and good functional group tolerance have been achieved. Besides, the synthetic potential of this reaction was highlighted by a gram-scale reaction and the one-pot diastereoselective synthesis of trifluoromethylated cyclopropanols.

Synthesis of Cyclopropenols Enabled by Visible-Light-Induced Organocatalyzed [2+1] Cyclization

Although the synthesis of common cyclopropenes has been well studied, the access to cyclopropenols is rather limited. Herein, we report the first synthesis of α-trifluoromethylated cyclopropenols via 2+1 cycloaddition reactions between alkynes and trifluoroacylsilanes, enabled by visible-light-induced organocatalysis. The novel ambiphilic donor-acceptor carbenes derived from trifluoroacetylsilanes reacted efficiently with both activated and non-activated alkynes. The reaction features simple operation, mild conditions, broad substrate scope and good functional group tolerance. The synthetic potential of the reaction is highlighted by the gram-scale reactions and first synthesis of α-trifluoromethylated cyclopropanols through the combination of the 2+1 cyclization and high diastereoselective hydrogenation reaction in one pot.

Phosphine-Catalyzed Dearomative [3 + 2] Cycloaddition of Benzoxazoles with a Cyclopropenone

The triphenylphosphine-catalyzed dearomative [3 + 2] cycloaddition of benzoxazoles with 1,2-diphenylcyclopropenone is herein described. The reaction scope, mechanism, and possible future applications of this rare organocatalyzed cycloaddition are herein discussed.

Catalytic regio- and stereoselective silicon–carbon bond formations on unsymmetric gem-difluorocyclopropenes by capture of silyl metal species

A highly regioselective silylation of unsymmetric gem-difluorocyclopropenes was achieved by the capture of in-situ formed silyl metal intermediates, which gave structurally diverse silyldifluorocyclopropanes with good yields and stereoselectivity.

Rhodium-Catalyzed Dearomative Rearrangement of 2-Oxypyridines with Cyclopropenes: Access to N-Alkylated 2-Pyridones

A rhodium-catalyzed dearomative O-to-N rearrangement reaction of 2-oxypyridines has been developed by using cyclopropenes as the carbene precursors. This protocol features broad substrate scope and mild reaction conditions, providing a...

Catalytic Carbochlorocarbonylation of Unsaturated Hydrocarbons via C-COCl Bond Cleavage*

Here we report a palladium‐catalysed difunctionalisation of unsaturated C−C bonds with acid chlorides. Formally, the C−COCl bond of an acid chloride is cleaved and added, with complete atom economy, across either strained alkenes or a tethered alkyne to generate new acid chlorides. The transformation does not require exogenous carbon monoxide, operates under mild conditions, shows a good functional group tolerance, and gives the isolated products with excellent stereoselectivity. The intermolecular reaction tolerates both aryl‐ and alkenyl‐substituted acid chlorides and is successful when carboxylic acids are transformed to the acid chloride in situ. The reaction also shows an example of temperature‐dependent stereodivergence which, together with plausible mechanistic pathways, is investigated by DFT calculations. Moreover, we show that benzofurans can be formed in an intramolecular variant of the reaction. Finally, derivatisation of the products from the intermolecular reaction provides a highly stereoselective approach for the synthesis of tetrasubstituted cyclopentanes.