Alkynyl Aziridines Research Articles

Visible light promoted synthesis of allenes

This review article summarizes the visible light mediated synthesis of allenes from substrates like 1,3-enynes, propargylic carbonates, homopropargylic alcohols, propargylic oxalates, alkynyl diazo compounds, and terminal alkynyl aziridines.

Kinetically Controlled Radical Addition/Elimination Cascade: From Alkynyl Aziridine to Fluorinated Allenes.

A kinetically controlled radical addition/elimination reaction generating fluorinated allenes was developed. This strategy offers a route to a facile synthesis of diverse trifluoromethyl, difluoromethylene, and perfluoroalkyl functionalized allenes from readily available fluoroalkyl halides and alkynyl aziridines under visible-light irradiation. Density functional theory calculation of this radical clock type of reaction revealed a kinetically controlled C-N bond cleavage overcoming the alternative thermodynamically controlled C-C bond cleavage process.

Fluorinated triazole-containing sphingosine analogues. Syntheses and in vitro evaluation as SPHK inhibitors.

Sphingosine analogues with a rigid triazole moiety in the aliphatic chain and systematic modifications in the polar head and different degrees of fluorination at the terminus of the alkylic chain were synthesized from a common alkynyl aziridine key synthon. This key synthon was obtained by enantioselective organocatalyzed aziridination and it was subsequently ring opened in a regioselective manner in acidic medium. Up to 16 sphingosine analogues were prepared in a straightforward manner. The in vitro activity of the obtained products as SPHK1 and SPHK2 inhibitors was evaluated, displaying comparable activity to that of DMS.

ChemInform Abstract: Catalytic Asymmetric Synthesis of Alkynyl Aziridines: Both Enantiomers of cis‐Aziridines from One Enantiomer of the Catalyst.

Alkynyl aziridines can be obtained from the catalytic asymmetric aziridination (AZ reaction) of alkynyl imines with diazo compounds in high yields and high asymmetric inductions mediated by a chiral boroxinate or BOROX catalyst. In contrast to the AZ reaction with aryl- and alkyl-substituted imines, alkynyl imines react to give cis-substituted aziridines with both diazo esters and diazo acetamides. Remarkably, however, the two diazo compounds give different enantiomers of the cis-aziridine from the same enantiomer of the catalyst. Theoretical considerations of the possible transition states for the enantiogenic step reveal that the switch in enantiomers results from a switch from Si-face to Re-face addition to the imine, which in turn is related to a switch from reaction with an E-imine in the former and a Z-isomer of the imine in the latter.

Catalytic asymmetric synthesis of alkynyl aziridines: both enantiomers of cis-aziridines from one enantiomer of the catalyst.

Alkynyl aziridines can be obtained from the catalytic asymmetric aziridination (AZ reaction) of alkynyl imines with diazo compounds in high yields and high asymmetric inductions mediated by a chiral boroxinate or BOROX catalyst. In contrast to the AZ reaction with aryl- and alkyl-substituted imines, alkynyl imines react to give cis-substituted aziridines with both diazo esters and diazo acetamides. Remarkably, however, the two diazo compounds give different enantiomers of the cis-aziridine from the same enantiomer of the catalyst. Theoretical considerations of the possible transition states for the enantiogenic step reveal that the switch in enantiomers results from a switch from Si-face to Re-face addition to the imine, which in turn is related to a switch from reaction with an E-imine in the former and a Z-isomer of the imine in the latter.

ChemInform Abstract: Air‐ and Moisture‐stable Amphoteric Molecules: Enabling Reagents in Synthesis

AbstractReview: 51 refs.

Air- and Moisture-Stable Amphoteric Molecules: Enabling Reagents in Synthesis

Researchers continue to develop chemoselective synthesis strategies with the goal of rapidly assembling complex molecules. As one appealing approach, chemists are searching for new building blocks that include multiple functional groups with orthogonal chemical reactivity. Amphoteric molecules that possess nucleophilic and electrophilic sites offer a versatile platform for the development of chemoselective transformations. As part of a program focused on new methods of synthesis, we have been developing this type of reagents. This Account highlights examples of amphoteric molecules developed by our lab since 2006. We have prepared and evaluated aziridine aldehydes, a class of stable unprotected α-amino aldehydes. Structurally, aziridine aldehydes include both a nucleophilic amine nitrogen and an electrophilic aldehyde carbon over the span of three atoms. Under ambient conditions, these compounds exist as homochiral dimers with an aziridine-fused five-membered cyclic hemiaminal structure. We have investigated chemoselective reactions of aziridine aldehydes that involve both the aziridine and aldehyde functionalities. These transformations have produced a variety of densely functionalized nitrogen-containing compounds, including amino aldehydes, 1,2-diamines, reduced hydantoins, C-vinyl or alkynyl aziridines, and macrocyclic peptides. We have also developed air- and moisture-stable α-boryl aldehydes, another class of molecules that are kinetically amphoteric. The α-boryl aldehydes contain a tetracoordinated N-methyliminodiacetyl (MIDA) boryl substituent, which stabilizes the α-metalloid carbonyl system and prevents isomerization to its O-bond enolate form. Primarily taking advantage of chemoselective transformations at the aldehyde functionality, these α-boryl aldehydes have allowed us to synthesize a series of new functionalized boron-containing compounds that are difficult or impossible to prepare using established protocols, such as α-borylcarboxylic acids, boryl alcohols, enol ethers, and enamides. Using α-borylcarboxylic acids as starting materials, we have also prepared several new amphoteric borylated reagents, such as α-boryl isocyanates, isocyanides, and acylboronates. These compounds are versatile building blocks in their own right, enabling the rapid synthesis of other boron-containing molecules.

Synthesis of crambescin B carboxylic acid, a potent inhibitor of voltage-gated sodium channels

The stereocontrolled synthesis of a racemic carboxylic acid of crambescin B, a marine alkaloid, is described. The synthesis features two highly stereoselective reactions: (I) palladium-catalyzed hydroxymethylation of an alkynyl aziridine having an N-guanidino group and (II) cascade bromocyclization providing a spiro-hemiaminal structure. The cell-based colorimetric assay showed that the synthesized carboxylic acid exhibited a potent inhibitory activity on voltage-gated sodium channels.

Isotopic labelling studies for a gold-catalysed skeletal rearrangement of alkynyl aziridines

Isotopic labelling studies were performed to probe a proposed 1,2-aryl shift in the gold-catalysed cycloisomerisation of alkynyl aziridines into 2,4-disubstituted pyrroles. Two isotopomers of the expected skeletal rearrangement product were identified using 13C-labelling and led to a revised mechanism featuring two distinct skeletal rearrangements. The mechanistic proposal has been rationalised against the reaction of a range of 13C- and deuterium-labelled substrates.

ChemInform Abstract: An Efficient and Selective Synthesis of 2,5‐Substituted Pyrroles by Gold‐Catalyzed Ring Expansion of Alkynyl Aziridines.

AbstractIn the case of silylated alkynes like (V), desilylation takes place giving 2‐substituted pyrroles such as (VI).

An efficient and selective synthesis of 2,5-substituted pyrroles by gold-catalysed ring expansion of alkynyl aziridines

A range of substituted alkynyl aziridines undergo a ring expansion to afford 2,5-substituted pyrroles under gold catalysis. While effective conditions can be generated from other gold sources, a combination of Ph 3PAuCl and AgOTs generate a catalyst system that provides extremely clean cycloisomerisation reactions requiring minimal work-up and purification.

ChemInform Abstract: Counterion Effects in a Gold‐Catalyzed Synthesis of Pyrroles from Alkynyl Aziridines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Counterion Effects in a Gold-Catalyzed Synthesis of Pyrroles from Alkynyl Aziridines

Aryl-substituted N-tosyl alkynyl aziridines undergo a gold-catalyzed ring expansion to afford 2,5-substituted pyrrole products. Under certain conditions, a ring-expansion and rearrangement leads to 2,4-substituted pyrroles. The reaction pathway is determined by the counterion to the gold catalyst.