Sigmatropic Rearrangement of Vinyl Aziridines: Expedient Synthesis of Cyclic Sulfoximines from Chiral Sulfinimines

A novel rearrangement of 2‐vinyl aziridine 2‐carboxylates to unusual chiral cyclic sulfoximines is described herein. The method allows the synthesis of substituted cyclic sulfoximines in high yields with complete stereocontrol, and tolerates a wide substrate scope. A one‐pot process starting directly from sulfinimines provides access to complex chiral sulfoximines in only two steps from commercially available aldehydes. A mechanistic hypothesis and synthetic application in the formal synthesis of trachelanthamidine, by transformation of a cyclic sulfoximine into a pyrroline, is also disclosed.     

Anionic cross-coupling reaction of alpha-metallated alkenyl sulfoximines and alkenyl sulfoximines with cuprates featuring a 1,2-metal-ate rearrangement of sulfoximine-substituted higher order alkenyl cuprates and an alpha-metallation of alkenyl sulfoximines by cuprates

(E)- and (Z)-configured alpha-lithioalkenyl sulfoximines, which are available through lithiation of the corresponding alkenyl sulfoximines, undergo a anionic cross-coupling reaction (ACCR) with organocuprates with formation of the corresponding alkenyl cuprates and sulfinamide. The alkenyl cuprates can be trapped by electrophiles. The ACCR presumably proceeds via the formation of a higher-order sulfoximine-substituted alkenyl cuprate, which undergoes a 1,2-metal-ate rearrangement whereby the sulfoximine group acts as the nucleofuge. The parent (E)- and (Z)-configured alkenyl sulfoximines suffer upon treatment with an organocuprate a deprotonation at the alpha-position with formation of the corresponding alpha-cuprioalkenyl sulfoximines. These derivatives also enter into a similar ACCR with organocuprates. The ACCR of sulfoximines substituted homoallylic alcohols allows a stereoselective access to enantio- and diastereopure substituted homoallylic alcohols.     

Increasing Complexity: A Practical Synthetic Approach to Three-Dimensional,Cyclic Sulfoximines and First Insights into Their in Vitro Properties

A short synthetic approach with broad scope to access five- to seven-membered cyclic sulfoximines in only two to three steps from readily available thiophenols is reported. Thus, simple building blocks were converted to complex molecular structures by a sequence of S-alkylation and one-pot sulfoximine formation, followed by intramolecular cyclization. Seventeen structurally diverse cyclic sulfoximines were prepared in high overall yields. In vitro evaluation of these underrepresented, three-dimensional, cyclic sulfoximines with respect to properties relevant to medicinal chemistry did not reveal any intrinsic flaw for application in drug discovery.     

Imination of sulfoxides mediated by IBX with Sc(OTf)3 as catalyst

Herein we utilized, for the first time, 2-iodoxybenzoate along with scandium triflate as a specific oxidant for PhthNH₂ to create sulfoximines. This method efficiently effects imination of aryl, benzyl, cyclic and alkyl substituted S?O bonds with good to excellent yields. In addition, sterically encumbered sulfoxides have been studied and found that the present protocol is the worthy choice. This facile method does not require either inert atmosphere or anhydrous solvents.     

Asymmetric synthesis of highly substituted gamma-amino acids from allyltitanium sulfoximines

[structure: see text]. Asymmetric syntheses of the highly substituted protected gamma-amino acids 10a, 10b, 18, and 21 have been developed starting from the allyltitanium sulfoximines V and VI, respectively, and furan-2-carbaldehyde.     

Regio- and Enantioselective Substitution of Acyclic Allylic Sulfoximines with Butylcopper in the Presence of Lithium Iodide and Boron Trifluoride

Enantiomerically pure N-methyl-, N-benzyl-, and N-(methoxyethyl)-S-(phenyl)cinnamylsulfoximines as well as the corresponding crotylsulfoximines have been prepared from N-methyl-, N-benzyl-, and N-(methoxyethyl)-S-(lithiomethyl)sulfoximines and carbonyl compounds by an addition-elimination-isomerization reaction sequence. Under basic conditions, complete isomerization of the vinylic sulfoximines, obtained as intermediates, to the corresponding allylic sulfoximines takes place. Chromatographically separable mixtures of (E) and (Z) allylic sulfoximines were isolated in the case of beta,gamma-disubstituted allylic sulfoximines. The (E/Z) ratio depends on the nature of the substituents in the beta- and gamma-positions, and the equilibrium amount of the (Z) isomer varies from 68% to nil. The allylic N-methylsulfoximines do not racemize thermally, and their rearrangement to the corresponding allylic sulfinamides is negligible. Upon prolonged treatment with boron trifluoride at low temperatures allylic N-methylsulfoximines are recovered unchanged. The crystal structure of S-(3,4-dihydronaphthalen-2-ylmethyl)-N-methyl-S-phenylsulfoximine was determined. Reaction of the allylic sulfoximines with butylcopper in the presence of lithium iodide and boron trifluoride leads with very high gamma-selectivities and moderate to high enantioselectivities to the corresponding chiral alkenes. Their configuration was determined by chemical correlation through ozonolysis to the corresponding carbonyl compounds. The asymmetric induction exerted by the chiral N-methyl-S-phenylsulfoximine group strongly depends on the double bond configuration and the substituents in the beta- and gamma-positions. The (E) allylic sulfoximines are substituted with low to moderate enantioselectivities (2-66%), whereas the (Z) allylic sulfoximines react with much higher enantioselectivities (69-92%). Interestingly, substitution of the beta-methyl-gamma-phenyl-substituted (Z) allylic sulfoximine and its beta-phenyl-gamma-methyl isomer proceeded with almost the same degree of asymmetric induction but with the opposite sense. Replacement of the N-methyl group by a benzyl or a methoxyethyl group has no significant influence on the regio- and enantioselectivity of the substitution.     

Cover Feature: Fluoroalkyl Sulfoximines for Versatile Photocatalytic Radical Fluoroalkylations (Chem. Rec. 9/2023)

Fluoroalkyl sulfoximines, which serve as electron-accepting fluoroalkyl radical sources, are easy-to-handle, solid, and bench-stable chemicals. Fluoroalkyl radicals can be generated from sulfoximine reagents using strong one-electron injectors, such as a highly reducing photoredox catalyst in the excited state. Our group has developed photocatalytic radical di- and mono-fluoromethylation and α-monofluoroalkylation of olefins with the corresponding fluoroalkyl sulfoximines. In this personal account, appropriate combinations of fluoroalkyl sulfoximines and photoredox catalysts, leading to successful radical fluoroalkylation, have been discussed.     

Efficient Synthesis of Cyclic Sulfoximines from N-Propargylsulfinamides through Sulfur–Carbon Bond Formation

Cyclic sulfoximines were readily synthesized by the cyclization of N-propargylsulfinamides without using expensive and toxic metal catalysts. This cyclization proceeded without loss of optical purity of chiral sulfinamides through the unusual sulfur–carbon bond formation promoted by an inexpensive inorganic base. This stereospecific cyclization offers a general approach to the asymmetric synthesis of chiral cyclic sulfoximines as an emerging heterocycle in medicinal chemistry.     

Applications of the Ugi reaction with ketones

A convenient synthesis of highly functionalized, α,α-disubstituted amino acid amide derivatives has been accomplished by using cyclic and acyclic ketones as the carbonyl inputs in the Ugi multicomponent reaction. An application of this extension of the Ugi reaction to the synthesis of α,α-divinyl amino acids that may be cyclized via ring-closing metathesis to provide highly substituted pyrrolidines is described.     

Modular asymmetric synthesis of functionalized azaspirocycles based on the sulfoximine auxiliary

A modular asymmetric synthesis of the functionalized azaspirocycles 6 (m = 2, n = 1), 7 (m = 1, n = 2), 8 (m = n = 2), 12, 20, and 24 from the cyclic allylic sulfoximines 1 is described. The synthetic strategy is based on the stereoselective construction of the carbocycle 4 containing the amino-substituted tertiary C atom from 1 followed by the generation of the azaspirocycle. Three different routes have been followed for the synthesis of the heterocyclic ring: N,C-dianion cycloalkylation, ring-closing metathesis, and N-acyl iminium ion formation.     

C-C bond-forming desulfurizations of sulfoximines

Highly substituted, enantiomerically pure azaheterocyclic ring systems play an important role in medicinal chemistry as potential peptide mimetics. Metalated 2-alkenyl sulfoximines offer an efficient entry to this class of compounds. In this paper, we describe a new means to remove the sulfonimidoyl auxiliary with concomitant formation of a C-C double bond.     

Sulfoximidations of Benzylic C−H bonds by Photocatalysis

An efficient photocatalytic functionalization of compounds with benzylic C?H bonds by sulfoximidation in visible light is described. The mild reaction conditions allow the use of a broad array of substrates, including diarylmethane, alkyl arenes, arylacetonitrile, 2‐arylacetate, and alkynyl aryl methanes. The sulfoximidation process is highly chemoselective and leads to the corresponding sulfoximines in generally good yields. Mechanistic investigations suggested the intermediacy of sulfoximidoyl radicals.     

Asymmetric synthesis of 2,3-dihydrofurans and of unsaturated bicyclic tetrahydrofurans through alpha-elimination and migratory cyclization of silyloxy alkenyl aminosulfoxonium salts. Generation and intramolecular O,Si-bond insertion of chiral disubstituted beta-silyloxy alkylidene carbenes

Treatment of the bis(allylsulfoximine)titanium complexes derived from the beta-methyl-substituted acyclic allylic sulfoximines 13a and 13b with aldehydes gave with high selectivities the corresponding sulfoximine-substituted homoallylic alcohols which were isolated as the silyl ethers 15a-h. Methylation of sulfoximines 15a-h afforded the aminosulfoxonium salts 5a-h which upon treatment with LiN(H)tBu gave in high yields the enantio- and diastereomerically pure silyl-substituted 2,3-dihydrofurans 4a-h. Treatment of the titanium complexes derived from the cyclic allylic sulfoximines 17a, 17b, and ent-17c with p-MeOC(6)H(4)CHO delivered with high selectivities the corresponding sulfoximine-substituted cyclic homoallylic alcohols which were isolated as the silyl ethers 18a, 18b, and ent-18c, respectively. Methylation of sulfoximines 18a, 18b, and ent-18c furnished the aminosulfoxonium salts 8a, 8b, and ent-8c, respectively, whose treatment with LiN(H)t-Bu gave the enantio- and diastereomerically pure fused bicyclic 2,3-dihydrofurans 6a, 6b, and ent-6c, respectively, in good yields. It is proposed that the 1-alkenyl aminosulfoxonium salts 5a-h, 8a, 8b, and ent-8c react with the base under alpha-elimination and formation of the acyclic and cyclic beta-silyloxy alkylidene carbenes 2a-h, 7a, 7b, and ent-7c, respectively, which then undergo a 1,5-O,Si-bond insertion and 1,2-silyl migration. The cyclic aminosulfoxonium salts 8a, 8b, and ent-8c upon treatment with 1,8-diazabicyclo[5.4.0]-7-undecene did not undergo an alpha-elimination but suffered a novel migratory cyclization with formation of the enantio- and diastereomerically pure bicyclic tetrahydrofurans 9a, 9b, and ent-9c, respectively. It is proposed that the 1-alkenyl sulfoxonium salts 8a, 8b, and ent-8c are isomerized to the allylic aminosulfoxonium salts 10a, 10b, and ent-10c, respectively, which then suffer an intramolecular substitution of the (dimethylamino)sulfoxonium group by the silyloxy group followed by a desilylation. The syntheses of the 2,3-dihydrofurans 4a-h, 6a, and 6b and of the tetrahydrofurans 9a and 9b are accompanied by the formation of sulfinamide 16 of >or=98% ee, which can be converted via sulfoxide 28 of >or=98% to the starting sulfoximine 11 of >or=98% ee.     

Asymmetric modular synthesis of highly functionalized medium-sized carbocycles and lactones via ring-closing metathesis of sulfoximine-substituted trienes

A modular asymmetric synthesis of medium-sized carbocycles and lactones has been developed that affords highly substituted 7-, 9-, and 11-membered rings. The key steps are (1) the highly diastereoselective synthesis of sulfoximine-substituted homoallylic alcohols from allylic sulfoximines and unsaturated as well as saturated aldehydes, (2) an E-stereoselective alkylation and hydroxyalkylation of sulfoximine-substituted alkenyllithium derivatives, (3) the esterification of sulfoximine-substituted homoallylic alcohols, and (4) the ring-closing metathesis reaction of sulfoximine-substituted trienes with the ruthenium catalyst 8. Two examples for the further synthetic elaboration of the sulfoximine-substituted carbocycles are provided. The selective cleavage of the tert-butyldimethylsilyl group of 12 in the presence of the triethylsilyl group afforded the allylic alcohol 18 which was oxidized to enone 19. A cross-coupling reaction of the sulfoximine-substituted carbocycle 9 with LiCuMe2 furnished the methyl-substituted derivative 20.     

Electrochemical imination of sulfoxides using N-aminophthalimide

[reaction: see text] A novel electrochemical sulfoxide imination process is described. Our approach starts with a highly selective nitrene transfer from N-aminophthalimide to a variety of sulfoxides. This oxidative treatment is followed by reductive N-N bond cleavage under the controlled current conditions, which leads to a range of parent NH sulfoximines. In addition to solving the challenging problem of removing the N-phthalimido group, the overall process avoids the use of toxic oxidants and metal additives.     

NEW METHODS FOR THE PREPARATION OF SULFOXIMINES

Abstract

Three methods that have been developed in our laboratory for the preparation of sulfoximines are described. Two of these involve the efficient, high yield oxidation of certain sulfilimines (iminosulfuranes) with ruthenium tetroxide (catalytic Ru0₂ + sodium periodate or hypochlorite cooxidant) and m-chloroperoxybenzoic acids, respectively, in biphasic systems. The third method is the direct preparation of sulfoximines from DMSO-t-butyl hypochlorite-aromatic amines. The scope and limitations of the procedures will be described.     

A Simple and Highly Efficient One-Pot Procedure for the Synthesis of Amides via Beckmann Rearrangements Using 1-Tosylimidazole (TsIm)

A facile and highly efficient method for one-pot Beckmann rearrangement of ketoximes into N-substituted amides using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, ketoximes are refluxed with TsIm and Cs₂CO₃ in the presence of SiO₂ as a recyclable catalyst in DMF affording the corresponding amides in high yields. This methodology is highly efficient and regioselective for various structurally diverse ketoximes including symmetrical and unsymmetrical as well as cyclic oximes. The results of quantum mechanical studies used to rationalize the experimental outcomes are discussed.     

A stereospecific synthesis of chiral cyclic sulfinamides

Treatment of racemic or enantiomerically pure 2,1-benzothiazines (cyclic sulfoximines) with lithium triethylborohydride results in clean loss of the S-aryl group with complete retention of configuration at sulfur to produce diastereomerically and/or enantiomerically pure cyclic sulfinamides in excellent yield.     

Iron‐Catalyzed Imidative Kinetic Resolution of Racemic Sulfoxides

Kinetic resolution of racemic sulfoxides requires either custom substrates or shows moderate enantioselectivity, leading to achiral coproducts (such as sulfones) as an intrinsic part of the process. A new strategy is demonstrated that allows the resolution of racemic sulfoxides through catalytic asymmetric nitrene‐transfer reactions. This approach gives rise to both optically active sulfoxides and highly enantioenriched sulfoximines. By using a chiral iron catalyst and a readily available iodinane reagent, high selectivity factors have been achieved under very practical reaction conditions. With respect to the substrate scope, it is noteworthy that this unprecedented imidative kinetic resolution of racemic sulfoxides provides access to both aryl–alkyl and dialkyl sulfoximines in highly enantioenriched forms.     

Nickel-Catalyzed Anionic Cross-Coupling Reaction of Lithium Sulfonimidoyl Alkylidene Carbenoids With Organolithiums

The mechanistic platform for a novel nickel⁰-catalyzed anionic cross-coupling reaction (ACCR) of lithium sulfonimidoyl alkylidene carbenoids (metalloalkenyl sulfoximines) with organometallic reagents is reported herein, affording substituted alkenylmetals and lithium sulfinamides. The Ni⁰-catalyzed ACCR of three different types of metalloalkenyl sulfoximines, including acyclic, axially chiral and exocyclic derivatives, with sp² organolithiums and sp² and sp³ Grignard reagents has been studied. The ACCR of metalloalkenyl sulfoximines with PhLi in the presence of the Ni⁰-catalyst and precatalyst Ni(PPh₃)₂Cl₂ afforded alkenyllithiums, under inversion of configuration at the C atom and complete retention at the S atom. In a combination of experimental and DFT studies, we propose a catalytic cycle of the Ni⁰-catalyzed ACCR of lithioalkenyl sulfoximines. Computational studies reveal two distinctive pathways of the ACCR, depending on whether a phosphine or 1,5-cyclooctadiene (COD) is the ligand of the Ni atom. They rectify the underlying importance of forming the key Ni⁰-vinylidene intermediate through an indispensable electron-rich Ni⁰-center coordinated by phosphine ligands. Fundamentally, we present a mechanistic study in controlling the diastereoselectivity of the alkenyllithium formation via the key lithium sulfinamide coordinated Ni⁰-vinylidene complex, which consequently avoids an unselective formation of an alkylidene carbene Ni-complex and ultimately racemic alkenyllithium.