Propargylic Sulfones Research Articles

TFA-Promoted Cascade Sulfonylation/Rearrangement/Cyclization of 1,5-Diynols and Sodium Sulfinates to Construct Sulfonylated Benzo[b]fluorenes.

A novel conversion of 1,5-diynols into sulfonylated benzo[b]fluorenes is reported by a TFA-promoted cascade cyclization with sodium sulfinates under mild conditions. This strategy provides an efficient and practical approach for accessing various sulfonated benzo[b]fluorenes in moderate to excellent yields under metal-free conditions. On the basis of the control experimental results and density functional theory calculations, a possible cascade transformation mechanism consisting of the dehydration of propargylic alcohols, sulfonylation, allenylation, and Schmittel-type cyclization is proposed. It is worth noting that TFA played an important role in this cascade cyclization, which promoted C-SO2R bond cleavage in a propargylic sulfone intermediate to form allenyl sulfones, followed by Schmittel-type cyclization to give the target product.

Copper-Catalyzed Enantioselective Trifluoromethoxylation of Propargyl Sulfonates.

Due to the strong electron-withdrawing nature and high lipophilicity of trifluoromethoxy group (OCF3 ), methods for introducing OCF3 into organic molecules are in high demand. However, the research area of direct enantioselective trifluoromethoxylation is still in the embryonic stage, with limited enantioselectivity and/or reaction types. Here, we describe the first copper-catalyzed enantioselective trifluoromethoxylation of propargyl sulfonates using trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxy source in up to 96 % ee.

Copper‐Catalyzed Enantioselective Trifluoromethoxylation of Propargyl Sulfonates

AbstractDue to the strong electron‐withdrawing nature and high lipophilicity of trifluoromethoxy group (OCF3), methods for introducing OCF3into organic molecules are in high demand. However, the research area of direct enantioselective trifluoromethoxylation is still in the embryonic stage, with limited enantioselectivity and/or reaction types. Here, we describe the first copper‐catalyzed enantioselective trifluoromethoxylation of propargyl sulfonates using trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxy source in up to 96 % ee.

Mechanistic Support for Intramolecular Migrative Cyclization of Propargyl Sulfones Provided by Catalytic Asymmetric Induction with a Chiral Counter Cation Strategy

AbstractWe previously reported an intramolecular migrative cyclization of propargylsufones and sulfonylalkynamides giving oxa‐ and azacycles, respectively. To confirm the postulated reaction mechanism, the reaction was conducted with chiral nucleophiles such as N‐heterocyclic carbenes, phosphines, and pyridines, or with sulfinate anions and chiral cations. As expected, migrative cyclization proceeded to give the enantiomerically enriched products. These results strongly support the postulated mechanism and provide the first example of the asymmetric version of this reaction.

Copper-Catalyzed Enantioselective Trifluoromethylthiolation of Secondary Propargyl Sulfonates

Although trifluoromethylthiolated compounds have privileged applications in pharmaceuticals and agrochemicals, efficient strategies for the asymmetric construction of Csp3–SCF3 bonds are limited. S...

Copper-Catalyzed Highly Enantioselective Difluoroalkylation of Secondary Propargyl Sulfonates with Difluoroenoxysilanes

Summary Despite the impressive progress recently made in transition-metal-catalyzed fluoroalkylation, the related asymmetric fluoroalkylation remains a challenging topic. Here, we report a copper-catalyzed highly enantioselective difluoroalkylation of secondary propargyl sulfonates using difluoroenoxysilanes. The reaction proceeds under mild reaction conditions with Cu(I)/PyBox as the catalyst. The advantages of this method include high efficiency, high enantioselectivity (enantiomeric ratio up to 99:1), and excellent functional-group tolerance. The resulting chiral propargylic α,α-difluoroketones can be transformed into enantiomerically enriched propargyl difluoromethylated compounds, providing a good platform for accessing a wide range of chiral difluoromethylated compounds that are of great interest in medicinal chemistry and materials science.

Copper‐Catalyzed Enantioselective Construction of Tertiary Propargylic Sulfones

AbstractTertiary propargylic sulfones are of significant importance in organic synthesis and medicinal chemistry, but to date no general asymmetric synthesis approach has been developed. We disclose a versatile copper‐catalyzed sulfonylation of propargylic cyclic carbonates using sodium sulfinates that allows the construction of propargylic sulfones featuring elusive quaternary stereocenters. This method provides the first successful example of such an enantioselective propargylic sulfonylation, features high asymmetric induction, wide functional group tolerance, and scalability, and enables attractive product diversification.

Copper-Catalyzed Enantioselective Construction of Tertiary Propargylic Sulfones.

Tertiary propargylic sulfones are of significant importance in organic synthesis and medicinal chemistry, but to date no general asymmetric synthesis approach has been developed. We disclose a versatile copper-catalyzed sulfonylation of propargylic cyclic carbonates using sodium sulfinates that allows the construction of propargylic sulfones featuring elusive quaternary stereocenters. This method provides the first successful example of such an enantioselective propargylic sulfonylation, features high asymmetric induction, wide functional group tolerance, and scalability, and enables attractive product diversification.

Sulfinate‐Organocatalyzed (3+2) Annulation Reaction of Propargyl or Allenyl Sulfones with Activated Imines

An operationally simple methodology for the synthesis of 4‐sulfonyl‐3‐pyrrolines is described using a propargylic sulfone and N‐sulfonyl imines as substrates. This annulation process is initiated by an arenesulfinate organocatalyst, which allows a smooth isomerization of the alkynyl precursor into the corresponding allene, followed by the generation of a highly reactive allyl sulfone anion. An asymmetric version involving an unprecedented enantiopure sulfinate–ammonium cooperative ion pair (PhSO2– R4N+*) was investigated. A proof‐of‐concept, with enantiomeric excesses of up to 41 %, was obtained according to a preliminary screening of commercially available chiral phase‐transfer catalysts.

Direct Substitution of Secondary and Tertiary Alcohols To Generate Sulfones under Catalyst- and Additive-Free Conditions

An environmentally benign protocol that affords propargylic sulfones containing highly congested carbon centers from easily accessible alcohols and sulfinic acids with water as the only byproduct is reported. The reaction proceeded via an in situ dehydrative cross-coupling process by taking advantage of the synergetic actions of multiple hydrogen bonds rather than relying on an external catalyst and/or additives to achieve high product distribution.

A Short Step Conversion of Alkynyl Propargyl Sulfones into Six-Membered Cyclic β-Ketosulfones via an Amine-Induced Novel Ring Closure

Alkynyl propargyl sulfones underwent secondary amine-induced cyclization to give six-membered cyclic enaminosulfones, and the products were subjected to acidic hydrolysis to afford the corresponding cyclic β-ketosulfones in high yields.

Copper-Catalyzed Highly Stereoselective Trifluoromethylation and Difluoroalkylation of Secondary Propargyl Sulfonates.

It is challenging to stereoselectively introduce a trifluoromethyl group (CF3 ) into organic molecules. To date, only limited strategies involving direct asymmetric trifluoromethylation have been reported. Herein, we describe a new strategy for direct asymmetric trifluoromethylation through the copper-catalyzed stereospecific trifluoromethylation of optically active secondary propargyl sulfonates. The reaction enables propargylic trifluoromethylation with high regioselectivity and stereoselectivity. The reaction could also be extended to stereospecific propargylic difluoroalkylation. Transformations of the resulting enantiomerically enriched fluoroalkylated alkynes led to a variety of chiral fluoroalkylated compounds, thus providing a useful protocol for applications in the synthesis of fluorinated complexes.

Copper-Catalyzed Highly Stereoselective Trifluoromethylation and Difluoroalkylation of Secondary Propargyl Sulfonates

Copper-Catalyzed Highly Stereoselective Trifluoromethylation and Difluoroalkylation of Secondary Propargyl Sulfonates

Phosphine-Promoted Migrative Cyclization of Sulfonylalkynol and Sulfonylalkynamide for the Synthesis of Oxa- and Azacycles

A catalytic amount of phosphine or DMAP promoted the migrative cyclization of propargyl sulfones bearing an internal nucleophilic functionality in a γ-umpolung manner.

Cu-catalyzed silylation of alkynes: a traceless 2-pyridylsulfonyl controller allows access to either regioisomer on demand.

The Cu-catalyzed silylation of terminal and internal alkynes bearing a 2-pyridyl sulfonyl group (SO2Py) at the propargylic position affords a breadth of vinyl silanes in good yields and with excellent regio- and stereocontrol under mild conditions. The directing SO2Py group is essential in terms of reaction efficiency and chemoselectivity. Importantly, this group also provides the ability to reverse the regiochemical outcome of the reaction, opening the access to either regioisomer without modification of the starting substrate by virtue of an in situ base-promoted alkyne to allene equilibration which takes place prior to the silylcupration process. Furthermore, removal of the directing SO2Py allows for further elaboration of the silylation products. In particular, a one-pot tandem alkyne silylation/allylic substitution sequence, in which both steps are catalyzed by the same Cu species, opens up a new approach for the access to either formal hydrosilylation regioisomer of unsymmetrical aliphatic-substituted internal alkynes from propargyl sulfones.

One-pot synthesis of aryl biaryl sulfones

Synthesis of aryl biaryl sulfones 3 with good yields is described. The one-pot efficient synthetic route is carried by the NaH-mediated tandem [C3+C3] annulations of cinnamaldehydes 1 and propargylic sulfones 2 under the boiling THF conditions.

Stereoselective synthesis of conjugated fluoro enynes.

Metalation-electrophilic fluorination of TMS- and TIPS-protected 1,3-benzothiazol-2-yl (BT) propargyl sulfones gave corresponding BT fluoropropargyl sulfones, Julia-Kocienski reagents for the synthesis of fluoro enynes. Both reagents reacted with aldehydes under mild DBU- or LHMDS-mediated conditions, giving high yields of conjugated fluoro enynes with E-stereoselectivity. In comparison to DBU-mediated reactions, stereoselectivity was higher in low-temperature LHMDS-mediated reactions. Two ketones were shown to react as well, using LHMDS as base. In situ removal of the TMS group gave terminal conjugated 2-fluoro 1,3-enynes. Synthetic utility of the fluoro enynes was demonstrated by conversion to internal alkynes and to stereoisomeric fluoro dienes via Sonogashira and Heck couplings.

ChemInform Abstract: Tertiary Amine Catalyzed Chemoselective and Asymmetric [3 + 2] Annulation of Morita—Baylis—Hillman Carbonates of Isatins with Propargyl Sulfones.

AbstractIn addition to propargyl sulfones, some activated olefins can also be used for the generation of spirocyclic oxindoles.

Tertiary Amine-Catalyzed Chemoselective and Asymmetric [3 + 2] Annulation of Morita–Baylis–Hillman Carbonates of Isatins with Propargyl Sulfones

A chemo- and enantioselective [3 + 2] annulation of Morita-Baylis-Hillman carbonates of isatins with propargyl sulfones was catalyzed by a β-ICD O-MOM ether 1c, affording spirocyclic 2-oxindoles bearing an unusual cyclopentadiene motif in outstanding ee values (up to >99%). More electrophiles, such as N-phenylmaleimide, have been also utilized to deliver complex spirocyclic 2-oxindoles with good results.

Reactions of Unsaturated Azides; Part 27:¹ Synthesis of 1,4-Diazidobuta-1,3-dienes

Three different methods to prepare 1,4-diazidobuta-1,3-dienes are presented: nucleophilic substitution of electron-poor dichlorinated substrates, nucleophilic addition of hydrazoic acid at an electron-deficient diallene, and a sequence of prototropic isomerizations of propargyl sulfones followed by nucleophilic additions. In all cases, isolation and assignment of the diastereomeric products was possible, and some sequential reactions, such as reduction or 1,3-dipolar cycloaddition of the azido groups, were performed.