Highly Regio- and Diastereoselective Anionic [3 + 2] Cycloaddition under Phase Transfer Catalytic Conditions

Visible-Light-Induced, Palladium-Mediated Desaturation/Sulfonation Cascade To Access 4-Sulfonyltetrahydropyridine Scaffolds

Herein, we report a visible-light-induced, palladium-catalyzed desaturation/sulfonation cascade, offering a concise route to a series of highly valuable 4-sulfonyltetrahydropyridine scaffolds from inexpensive and readily available piperidine derivatives with sodium sulfinates. The key to the success of this transformation is the well-designed sequence of palladium-mediated 1,5-hydrogen atom transfer/β-hydride elimination/allylic sulfonation process, which demonstrates the synthetic potentials for orchestrating synthetic events by rationally taking advantage of varied catalytic modes.

Ni-Catalyzed Asymmetric Reductive Alkenylation of α-Chlorosulfones with Vinyl Bromides

A nickel-catalyzed enantioconvergent reductive cross-coupling of α-chlorosulfones with vinyl bromides is described here. This strategy enables the enantioselective construction of chiral allylic sulfones from simple α-chlorosulfones and vinyl bromides. The mild reaction conditions lead to excellent functional group compatibility, as evidenced by the broad substrate scope and tolerance of complex bioactive molecules. Our preliminary mechanistic study suggests that this enantioselective vinylation process operates through a radical intermediate.

1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP)-Assisted Catalyst-Free Sulfonation of Allylic Alcohols with Sulfinyl Amides

A highly regioselective and catalyst-free sulfonation of allylic alcohols with sulfinyl amides has been realized. Such a mix-and-go procedure provides a convenient approach to synthetically various allylic sulfones under mild reaction conditions. Furthermore, this novel reaction shows ample substrate scope and outstanding functional group tolerance and could also be scaled-up. Meanwhile, it is the first example that sulfinyl amides act as a powerful sulfur nucleophile in the reactions. 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) as a solvent plays a critical role in allylic sulfonation.

Palladium-catalyzed regioselective hydrosulfonylation of allenes with sulfinic acids

A simple palladium-based catalytic system for hydrosulfonylation of allenamides was established. Various nitrogen-containing linear allylic sulfones can be generated in moderate to excellent yield with E-selectivity and 100% atom utilization.

Development of C2-Symmetric Chiral Spirocyclic Phase-Transfer Catalysts: Synthesis and Application to Asymmetric Alkylation of Glycinate Schiff Base

A class of C₂-symmetric chiral spirocyclic phase-transfer catalysts based on tetramethyl-1,1'-spirobiindane scaffold was synthesized from commercially available bisphenol A in 12 steps with 22-25% total yields, which features a more rigid and stable backbone and smaller dihedral angles and can be easily modified. These catalysts show high catalytic performance in the asymmetric alkylation of tert-butyl glycinate Schiff base at only 2 mol % catalyst loading, giving the target products with up to 92% yield and 98% ee.

Allylic C-S Bond Construction through Metal-Free Direct Nitroalkene Sulfonation

A metal-free, open-flask protocol was developed for the preparation of allylic sulfones through direct condensation of sodium arylsulfinates and β,β-disubstituted nitroalkenes. The key step of this process was the Lewis base-promoted equilibrium between nitroalkenes and allylic nitro compounds. Through this process, the readily available conjugated nitroalkenes can be easily converted into allylic nitro compounds, which contain more reactive C═C bonds toward the sulfonyl radical addition. As a result, allylic sulfones were prepared in excellent yields with a broad substrate scope under mild conditions.

Direct Regioselective [3 + 2]-Cyclization Reactions of Ambivalent Electrophilic/Nucleophilic β-Chlorovinyl Dithianes: Access to Cyclopentene Derivatives

The highly regioselective and operationally straightforward [3 + 2] cyclizations of β-chlorovinyl dithianes with α,β-unsaturated carbonyl compounds have been developed. This protocol provides direct access to highly functionalized cyclopentenes with perfect chemo- and regioselectivities under extremely mild reaction conditions. In particular, the unprecedented cyclization allows for the selective preparation of hydroxylated cyclopentenes.

Chiral Lithiated Allylic α-Sulfonyl Carbanions: Experimental and Computational Study of Their Structure, Configurational Stability, and Enantioselective Synthesis

X-ray crystal structure analysis of the lithiated allylic α-sulfonyl carbanions [CH2 CHC(Me)SO2 Ph]Li⋅diglyme, [cC6 H8 SO2 tBu]Li⋅PMDETA and [cC7 H10 SO2 tBu]Li⋅PMDETA showed dimeric and monomeric CIPs, having nearly planar anionic C atoms, only OLi bonds, almost planar allylic units with strong CC bond length alternation and the s-trans conformation around C1C2. They adopt a C1S conformation, which is similar to the one generally found for alkyl and aryl substituted α-sulfonyl carbanions. Cryoscopy of [EtCHCHC(Et)SO2 tBu]Li in THF at 164 K revealed an equilibrium between monomers and dimers in a ratio of 83:17, which is similar to the one found by low temperature NMR spectroscopy. According to NMR spectroscopy the lone-pair orbital at C1 strongly interacts with the CC double bond. Low temperature (6) Li,(1) H NOE experiments of [EtCHCHC(Et)SO2 tBu]Li in THF point to an equilibrium between monomeric CIPs having only OLi bonds and CIPs having both OLi and C1Li bonds. Ab initio calculation of [MeCHCHC(Me)SO2 Me]Li⋅(Me2 O)2 gave three isomeric CIPs having the s-trans conformation and three isomeric CIPs having the s-cis conformation around the C1C2 bond. All s-trans isomers are more stable than the s-cis isomers. At all levels of theory the s-trans isomer having OLi and C1Li bonds is the most stable one followed by the isomer which has two OLi bonds. The allylic unit of the C,O,Li isomer shows strong bond length alternation and the C1 atom is in contrast to the O,Li isomer significantly pyramidalized. According to NBO analysis of the s-trans and s-cis isomers, the interaction of the lone pair at C1 with the π* orbital of the CC double bond is energetically much more favorable than that with the "empty" orbitals at the Li atom. The C1S and C1C2 conformations are determined by the stereoelectronic effects nC -σSR * interaction and allylic conjugation. (1) H DNMR spectroscopy of racemic [EtCHCHC(Et)SO2 tBu]Li, [iPrCHCHC(iPr)SO2 tBu]Li and [EtCHC(Me)C(Et)SO2 tBu]Li in [D8 ]THF gave estimated barriers of enantiomerization of ΔG(≠) =13.2 kcal mol(-1) (270 K), 14.2 kcal mol(-1) (291 K) and 14.2 kcal mol(-1) (295 K), respectively. Deprotonation of sulfone (R)-EtCHCHCH(Et)SO2 tBu (94 % ee) with nBuLi in THF at -105 °C occurred with a calculated enantioselectivity of 93 % ee and gave carbanion (M)-[EtCHCHC(Et)SO2 tBu]Li, the deuteration and alkylation of which with CF3 CO2 D and MeOCH2 I, respectively, proceeded with high enantioselectivities. Time-dependent deuteration of the enantioenriched carbanion (M)-[EtCHCHC(Et)SO2 tBu]Li in THF gave a racemization barrier of ΔG(≠) =12.5 kcal mol(-1) (168 K), which translates to a calculated half-time of racemization of t1/2 =12 min at -105 °C.

Recent developments in asymmetric phase-transfer reactions

Phase-transfer catalysis has been recognized as a powerful method for establishing practical protocols for organic synthesis, because it offers several advantages, such as operational simplicity, mild reaction conditions, suitability for large-scale synthesis, and the environmentally benign nature of the reaction system. Since the pioneering studies on highly enantioselective alkylations promoted by chiral phase-transfer catalysts, this research field has served as an attractive area for the pursuit of "green" sustainable chemistry. A wide variety of asymmetric transformations catalyzed by chiral onium salts and crown ethers have been developed for the synthesis of valuable organic compounds in the past several decades, especially in recent years.