A General Method for the Preparation of N-Sulfonyl Aldimines and Ketimines

Azasulfur(iv) derivatives of sulfite and sulfinate esters by formal S-S bond insertion of dichloramines

Azasulfur(vi) compounds such as sulfoximines and sulfonimidamides are attractive due to the unique properties of the S[double bond, length as m-dash]N bond. While the synthesis of these carbon-attached sulfonimidoyl derivatives is well-established, the situation is different for their heteroatom-bound counterparts. In this work, we propose azasulfur(iv) esters as platform chemicals that can be derivatized to obtain all types of SVI[double bond, length as m-dash]N functional groups, among these are the poorly accessible, all-heteroatom imidosulfate esters. Using a chloroamination workflow established here, S-S bond-containing structures such as elemental sulfur or diaryl disulfides can be transformed into imidothionyl or sulfinimidoyl chlorides, which are easily esterified or amidated. Thus, chloramines serve as a versatile [N] and [Cl+] source, and by using them in the context reported here, we advance the set of mild synthetic methods as the latest toolbox member to cover even more of the azasulfur(iv) and (vi) chemical space.

Transsulfinamidation of Sulfinamides with Amines

Metal- and additive-free transsulfinamidation of N-unsubstituted sulfinamides and N-pivaloyl-protected sulfinamides with various amines is reported. With this method, both N-monosubstituted and N,N-disubstituted sulfinamides were obtained in good yields simply by heating. Preliminary experiments also indicate that alcohols can be used as nucleophiles instead of amines and can provide sulfinate esters.

Complementary strategies for synthesis of sulfinamides from sulfur-based feedstock

We describe a straightforward one-pot reductive protocol for the synthesis of sulfinamides from sulfonyl chlorides. This method enables the preparation of sulfinamides with a broad range of functional groups. Furthermore, we have expanded a known oxidative pathway to sulfinamides starting from thiols. These methods together provide a general strategy for the synthesis of sulfinamides from common sulfur-based feedstock that is available with large structural and functional group diversity.

Eco-friendly and efficient catalyst-free synthesis of N-sulfonylimines from sulfonamides and aldehydes: crucial role of Al2O3 as a reusable dehydrating agent

A green synthetic method for the synthesis of N-sulfonylimines was developed involving the straightforward condensation of sulfonamides with aldehydes under green and catalyst-free conditions, mediated by neutral Al₂O₃ as an efficient and reusable dehydrating agent. N-Sulfonylimines were produced in high yields and purity under simple experimental procedures.

Reversed-Polarity Synthesis of N-Sulfonyl Ketimines with Imidoylsilanes and Diaryliodonium Salts via Palladium-Catalyzed Reactions

Imines are important building blocks in organic chemistry. Iminines, aldimines and ketimines, have been traditionally synthesized by the condensation reaction of the corresponding carbonyl compound with an amine moiety. More recently, palladium-catalyzed synthesis of ketimines using imidoyl chlorides has been reported. As an alternative, we report the reversed-polarity synthesis of N-sulfonyl ketimines using an anion equivalent imidoylsilane as a new nucleophilic coupling partner in the presence of a palladium catalyst. To the best of our knowledge, this is the first report of the use of imidoylsilanes in transition-metal-catalyzed coupling reactions. Diaryliodonium salt as an electrophile, various aryl-aryl or heteroaryl-aryl N-sulfonyl ketimines were successfully prepared in up to 99% isolated yields.

Nickel-Catalyzed Kumada Cross-Coupling Reactions of Benzylic Sulfonamides

Herein, we report a Kumada cross-coupling reaction of benzylic sulfonamides. The scope of the transformation includes acyclic and cyclic sulfonamide precursors that cleanly produce highly substituted acyclic fragments. Preliminary data are consistent with a stereospecific mechanism that allows for a diastereoselective reaction.

Amide Iridium Complexes As Catalysts for Transfer Hydrogenation Reduction of N-sulfonylimine

Sulfonamide moieties widely exist in natural products, biologically active substance, and pharmaceuticals. Here, an efficient water-soluble amide iridium complexes-catalyzed transfer hydrogenation reduction of N-sulfonylimine is developed, which can be carried out under environmentally friendly conditions, affording a series of sulfonamide compounds in excellent yields (96-98%). In comparison with organic solvents, water is shown to be critical for a high catalytic transfer hydrogenation reduction in which the catalyst loading can be as low as 0.001 mol %. These amide iridium complexes are easy to synthesize, one structure of which was determined by single-crystal X-ray diffraction. This protocol gives an operationally simple, practical, and environmentally friendly strategy for synthesis of sulfonamide compounds.

Strategic Vinyl Sulfone Nucleophile β-Substitution Significantly Impacts Selectivity in Vinylogous Darzens and Aza-Darzens Reactions

Vinylogous Darzens and aza-Darzens reactions employing a benzothiophene 1,1-dioxide nucleophile are reported. These new [2 + 1] annulation reactions, which proceed under mild reaction conditions, are γ-selective, affording trans-epoxides selectively and favoring trans-aziridines. The reactions are base-dependent, with KOtBu and Cs₂CO₃ being optimal for aldehyde and imine annulations, respectively. Comparison of the benzothiophene nucleophile to its acyclic counterpart reveals superior performance in the case of aldehydes, while the outcome varies depending on the sulfonamide imine used.

Sulfinamide Synthesis Using Organometallic Reagents, DABSO, and Amines

We report the synthesis of sulfinamides using organometallic reagents, a sulfur dioxide reagent, and nitrogen based-nucleophiles. The addition of an organometallic reagent to the commercially available sulfur dioxide surrogate, DABSO, generates a metal sulfinate which is reacted with thionyl chloride to form a sulfinyl chloride intermediate. Trapping the sulfinyl chlorides in situ with a variety of nitrogen nucleophiles delivers sulfinamides in 32–83% yields. Each stage of the process is performed at room temperature, and the total reaction time is only 1.5 h.

Practical N-Hydroxyphthalimide-Mediated Oxidation of Sulfonamides to N-Sulfonylimines

A new method to prepare sulfonylimines through the oxidation of sulfonamides mediated by N-hydroxyphthalimide under mild conditions has been developed. Compared to reported oxidation methods, broader substrates scope and milder conditions were achieved in our method. Importantly, this oxidation method can afford N-sulfonyl enaminones using Mannich products as starting materials. Additionally, the one-pot Friedel-Crafts arylation reaction of unseparated N-sulfonylimine formed in our system with 1,3,5-trimethoxybenzene was successful without any additional catalyst.

Synthesis and identification of heteroaromatic N-benzyl sulfonamides as potential anticancer agents

Sulfonamides are a crucial class of bioisosteres that are prevalent in a wide range of pharmaceuticals, however, the available methods for their production directly from heteroaryl aldehyde reagents remains surprisingly limited. A new approach for regioselective incorporation of a sulfonamide unit to heteroarene scaffolds has been developed and is reported within. As a result, a variety of primary benzylic N-alkylsulfonamides have been prepared via a two-step (one pot) formation from the in situ reduction of an intermediate N-sulfonyl imine under mild, practical conditions. The compounds have been screened against a variety of cell lines for cytotoxicity effects using a Cell Titer Blue assay. The cell viability investigation identifies a subset of N-benzylic sulfonamides derived from the indole scaffold to be targeted for further development into novel molecules with potential therapeutic value. The most cytotoxic of the compounds prepared, AAL-030, exhibited higher potency than other well-known anticancer agents Indisulam and ABT-751.

An enantioselective aza-Henry reaction of trifluoromethyl ketimines catalyzed by phase-transfer catalysts

An enantioselective aza-Henry reaction of acyclic trifluoromethyl ketimines was performed using a bifunctional catalyst. The products were converted to diamines and imidazolidine-2-ones.

Highly enantioselective nitro-Mannich reaction of ketimines under phase-transfer catalysis

A novel bifunctional phase-transfer catalyst 1i was found to be highly efficient for the nitro-Mannich reaction of unactivated ketone-derived imines with the introduction of the protecting group 6-methyl-2-pyridylsulfonyl to the ketimines. Density functional theory (DFT) calculations are also performed to give the possible transition-state model.

Formation of N-sulfonyl imines from iminoiodinanes by iodine-promoted, N-centered radical sulfonamidation of aldehydes

A light-promoted, non-traditional carbonyl activation via a N-centered radical (NCR) species to produce activated imines using iminoiodinanes is reported.

Lewis acid-catalyzed tandem synthesis of 9-sulfonylamino- and 9-arylfluorenes

A Lewis acid-catalyzed three-step tandem synthesis of 9-arylfluorene was developed by simply heating a mixture of 2-formyl biphenyl, TsNCO and an arene.

Asymmetric synthesis of syn-propargylamines and unsaturated β-amino acids under Brønsted base catalysis

Propargylamines are important intermediates for the synthesis of polyfunctional amino derivatives and natural products and biologically active compounds. The classic method of synthesizing chiral propargylamines involves the asymmetric alkynylation of imines. Here, we report a significant advance in the catalytic asymmetric Mannich-type synthesis of propargylamines through catalytic asymmetric addition of carbon nucleophiles to C-alkynyl imines, culminating in a highly syn-selective catalytic asymmetric Mannich reaction of C-alkynyl imines that provide syn-configured propargylamines with two adjacent stereogenic centres and a transition metal-free organocatalytic asymmetric approach to β-alkynyl-β-amino acids with high efficiency and practicality, via a chiral Brønsted base-catalysed asymmetric Mannich-type reaction of in situ generated challenging N-Boc C-alkynyl imines from previously unreported C-alkynyl N-Boc-N,O-acetals, with α-substituted β-keto esters and less-acidic malonate (thio)esters as nucleophiles, respectively. A catalytic activation strategy is also disclosed, which may have broad implications for use in catalysis and synthesis.

Propargylamines are of interest both as biologically active compounds and versatile synthetic intermediates. Here, the authors report a method for the organocatalytic asymmetric synthesis of propargylamines through addition of carbon nucleophiles to alkynyl imines.

Nazarov cyclization of dienylaziridines: synthesis of cyclopentadienyl/hydrinedienyl/indenyl glycines

Cyclopentadienyl, hydrinedienyl, and indenyl glycines were synthesized by the Nazarov cyclization of dienylaziridines for the first time. Several substrates were synthesized to demonstrate the compatibility of this reaction. Asymmetric synthesis of these amino acids was also developed to show the additional scope of this method.

Synthesis of cis-C-iodo-N-tosyl-aziridines using diiodomethyllithium: reaction optimization, product scope and stability, and a protocol for selection of stationary phase for chromatography

The preparation of C-iodo-N-Ts-aziridines with excellent cis-diastereoselectivity has been achieved in high yields by the addition of diiodomethyllithium to N-tosylimines and N-tosylimine-HSO2Tol adducts. This addition-cyclization protocol successfully provided a wide range of cis-iodoaziridines, including the first examples of alkyl-substituted iodoaziridines, with the reaction tolerating both aryl imines and alkyl imines. An ortho-chlorophenyl imine afforded a β-amino gem-diiodide under the optimized reaction conditions due to a postulated coordinated intermediate preventing cyclization. An effective protocol to assess the stability of the sensitive iodoaziridine functional group to chromatography was also developed. As a result of the judicious choice of stationary phase, the iodoaziridines could be purified by column chromatography; the use of deactivated basic alumina (activity IV) afforded high yield and purity. Rearrangements of electron-rich aryl-iodoaziridines have been promoted, selectively affording either novel α-iodo-N-Ts-imines or α-iodo-aldehydes in high yield.

Synthesis-guided structure revision of the sarcodonin, sarcoviolin, and hydnellin natural product family

A sweeping structural revision of the sarcodonin natural product family (published structures 1a-13a) is proposed after extensive studies aimed at their chemical synthesis. Key features of revised structure 1b include replacement of the N,N-dioxide moiety with an oxime, ring-opening of the central diketopiperazine, and transposition of the terphenyl wing from the 1β-2β position of 1a to the 2β-3β position of 1b. This structure revision arose from the serendipitous synthesis of a benzodioxane aminal (44) whose structure was unambiguously determined by X-ray crystallography and whose spectral properties bore considerable resemblance to the published data for the sarcodonins. A versatile new method for O-arylation of hydroxamic acids is also reported herein, as well as a manganese(III)-mediated α-oxidation of hydroxamic acids to aminals.