Synthesis of 1,2-Diamines from Vinyl Sulfonium Salts and Arylamines

Iron(II)-Catalyzed 1,2-Diamination of Styrenes Installing a Terminal NH2 Group Alongside Unprotected Amines

1,2-Diamination of alkenes represents an attractive way to generate differentiated vicinal diamines, which are prevalent motifs in biologically active compounds and catalysts. However, existing methods are usually limited in scope and produce diamines where one or both nitrogens are protected, adding synthetic steps for deprotection and further N-functionalization to reach a desired target. Furthermore, the range of amino groups that can be introduced at the internal position is fairly limited. Here we describe a 1,2-diamination of styrenes that directly installs a free amino group at the terminal position and a wide variety of unprotected nitrogen nucleophiles (primary or secondary alkyl or aromatic amines, sulfoximines, N-heterocycles, and ammonia surrogate) at the internal position. Two complementary sets of conditions encompass electronically activated and deactivated styrenes with diverse substitution patterns and functional groups. Moreover, this strategy can be extended to the 1,2-aminothiolation of styrenes.

Recent Applications of Sulfonium Salts in Synthesis and Catalysis

The use of sulfonium salts in organic synthesis has experienced a dramatic increase during the last years that can arguably be attributed to three main factors; the development of more direct and efficient synthetic methods that make easily available sulfonium reagents of a wide structural variety, their intrinsic thermal stability, which facilitates their structural modification, handling and purification even on large scale, and the recognition that their reactivity resembles that of hypervalent iodine compounds and therefore, they can be used as replacement of such reagents for most of their uses. This renewed interest has led to the improvement of already existing reactions, as well as to the discovery of unprecedented transformations; in particular, by the implementation of photocatalytic protocols. This review aims to summarize the most recent advancements on the area focusing on the work published during and after 2020. The scope of the methods developed will be highlighted and their limitations critically evaluated.

Ring-Opening Sulfonylation of Cyclic Sulfonium Salts with Sodium Sulfinates under Transition-Metal- and Additive-Free Conditions

Incorporating a sulfonyl group into parent molecules has been shown to effectively improve their synthetic applications and bioactivities. In this study, we present a straightforward and practical approach for the ring-opening reaction of alkenyl-aryl sulfonium salts with sodium sulfinates to produce a range of sulfur-containing alkyl sulfones. This method offers the benefits of mild reaction conditions, easily accessible raw materials, wide substrate applicability, good functional group compatibility, and operational simplicity. Importantly, the resulting products can be readily converted into sulfoxides, sulfones, sulfoximines, and some heterocyclic compounds.

Base-Mediated Divergent Synthesis of Spiro-heterocycles Using Pronucleophiles and Ethylene via Thianthrenation

Spirocyclic compounds are abundant in biologically active products. However, the divergent synthesis of spirocyclic compounds using low-cost and abundant available starting materials remains a challenge. Herein, we report an effective method for producing spirocyclic motifs using a cyclic β-carbonyl ester or amide and ethylene via thianthrenation. This strategy highlights the exciting possibility of utilizing abundant ethylene as a C-2 synthon and allows regulating the core structure of the spirocyclic compound by simply altering the base type.

Synthesis of alkynyl sulfides via base-promoted nucleophilic ring-opening of α-bromostyrene sulfonium salt

An efficient method for the synthesis of alkynyl sulfides via a C(sp3)-S bond cleavage of α-bromostyrene sulfonium salts has been developed. This base-promoted nucleophilic ring-opening pathway allows the preparation of diverse alkynyl sulfide compounds using tetramethylene sulfoxide as the sulfur source. The reaction proceeds with good functional group tolerance and could be applied to the late-stage functionalization of bioactive molecules and drugs. Furthermore, the synthetic utility of this method was demonstrated by a one-pot synthesis, scale-up reaction and further modification of various alkynyl sulfide products.

Photoredox-catalyzed unsymmetrical diamination of alkenes for access to vicinal diamines

A photoredox-catalyzed unsymmetrical diamination of alkenes by using N-aminopyridinium salts and nitriles as the amination reagents has been developed. Various vicinal diamines were obtained in moderate to excellent yields under mild reaction conditions. Furthermore, this protocol could be applied in the late-stage modification of pharmaceuticals and natural products. Preliminary mechanistic studies suggested that this methodology may undergo a radical pathway followed by a Ritter-type reaction.

Base-Promoted Ring-Opening Hydroxylation of Cyclic Sulfonium Salts

Herein, we reported a general strategy for the synthesis of sulfur-containing primary alcohol derivatives by base-promoted ring-opening hydroxylation of cyclic sulfonium salts. A variety of sulfonium salts were successfully transformed into the desired hydroxylated products in moderate to excellent yields with good functional group tolerance. Moreover, the one-pot synthesis, scale-up reaction, and late-stage functionalization of complex molecules demonstrated the practicability of this synthetic protocol in the field of synthetic chemistry.

Dithiolation of Alkenyl Sulfonium Salts with Arylthiols to Access 1,2-Dithioalkanes

A dithiolation of alkenyl sulfonium salts with arylthiols is described, affording a series of 1,2-dithioalkanes in high yields. This protocol features mild and catalyst-free conditions and involves the formation of two C-S bonds sequentially via the regioselective addition of an arylthiol to the unsaturated C═C bonds, followed by the attack of another arylthiol to form 1,2-dithioalkanes exclusively.

Ring Opening of Aziridines by Pendant Sulfamates Allows for Regioselective and Stereospecific Preparation of Vicinal Diamines

The ring opening of aziridines by pendant sulfamates is a viable strategy for the rapid preparation of vicinal diamines. Our reaction is compatible with both disubstituted cis- and trans-aziridines; unsubstituted, N-alkyl, and N-aryl sulfamates engage effectively. In all cases examined, the cyclization reaction is perfectly regioselective and stereospecific. Once activated, the product oxathiazinane heterocycles can be ring opened with a diverse range of nucleophiles.

Regioselective Synthesis of N-Vinyl Pyrazoles from Vinyl Sulfonium Salts with Diazo Compounds

Herein, we develop a base-promoted regioselective synthesis of N-vinyl pyrazoles from vinyl sulfonium salts with diazo compounds. This metal-free synthetic protocol provides an efficient and practical approach to diverse N-vinyl pyrazoles in good to excellent yields under mild conditions. The reaction appears to experience a [3 + 2] annulation of vinyl sulfonium salts and diazo anions rather than diazo compounds, followed by N-vinylation.

Regiospecific Alkene Aminofunctionalization via an Electrogenerated Dielectrophile

Modular strategies to rapidly increase molecular complexity have proven immensely synthetically valuable. In principle, transformation of an alkene into a dielectrophile presents an opportunity to deliver two unique nucleophiles across an alkene. Unfortunately, the selectivity profiles of known dielectrophiles have largely precluded this deceptively simple synthetic approach. Herein, we demonstrate that dicationic adducts generated through electrolysis of alkenes and thianthrene possess a unique selectivity profile relative to more conventional dielectrophiles. Specifically, these species undergo a single and perfectly regioselective substitution reaction with phthalimide salts. This observation unlocks an appealing new platform for aminofunctionalization reactions. As an illustrative example, we implement this new reactivity paradigm to address a longstanding synthetic challenge: alkene diamination with two distinct nitrogen nucleophiles. Studies into the mechanism of this process reveal a key alkenyl thianthrenium salt intermediate that controls the exquisite regioselectivity of the process and highlight the importance of proton sources in controlling the reactivity of alkenyl sulfonium salt electrophiles.

Recent Advancements on Metal-Free Vicinal Diamination of Alkenes: Synthetic Strategies and Mechanistic Insights

The oxidative aminative vicinal difunctionalization of alkenes or related chemical feedstocks has emerged as sustainable and multipurpose strategies that can efficiently construct two -N bonds, and simultaneously prepare the synthetically fascinating molecules and catalysis in organic synthesis that typically required multi-step reactions. This review summarized the impressive breakthroughs on synthetic methodologies (2015-2022) documented especially over inter/intra-molecular vicinal diamination of alkenes with electron-rich or deficient diverse nitrogen sources. These unprecedented strategies predominantly involved iodine-based reagents/catalysts, which resent the interest of organic chemists due to their impressive role as flexible, non-toxic, and environmentally friendly reagents, resulting in a wide variety of synthetically useful organic molecules. Moreover, the information collected also describes the significant role of catalyst, terminal oxidant, substrate scope, synthetic applications, and their unsuccessful results to highlight the limitations. Special emphasis has been given to proposed mechanistic pathways to determine the key factors governing the issues of regioselectivity, enantioselectivity, and diastereoselectivity ratios.