One-pot synthesis of carbamates and thiocarbamates from Boc-protected amines

Na2CO3-promoted synthesis of thiocarbamates from isocyanates and thiols under mild conditions

Here, we developed an efficient method for the synthesis of s-alkyl or aryl thiocarbamates catalyzed by Na2CO3 under mild conditions using alkyl or aryl isocyanates and thiophenols or thiols. In situ reaction with deuterated tetrahydrofuran (d8-THF) was carried out to investigate the reaction mechanism. This method has the advantages of high yield, good functional group tolerance and high atom economy.

Direct synthesis of carbamates, thiocarbamates, and ureas from Boc-protected amines: a sustainable and efficient approach

In the quest for sustainable and efficient synthetic methodologies within medicinal chemistry, the synthesis of carbamates and their derivatives holds a pivotal role due to their widespread application in bioactive compounds. This investigation unveils a novel methodology for the straightforward transformation of Boc-protected amines into carbamates, thiocarbamates, and ureas, utilizing tert-butoxide lithium as the sole base. This approach effectively obviates the necessity for hazardous reagents and metal catalysts, presenting marked enhancements compared to traditional synthetic pathways. Notably, the method demonstrates facile scalability to gram-level production. This study contributes to the advancement of sustainable synthetic methodologies, offering a more benign and efficient alternative for the synthesis of key chemical intermediates with implications for broad pharmaceutical and agrochemical applications.

Direct C-H Sulfuration: Synthesis of Disulfides, Dithiocarbamates, Xanthates, Thiocarbamates and Thiocarbonates

In light of the important biological activities and widespread applications of organic disulfides, dithiocarbamates, xanthates, thiocarbamates and thiocarbonates, the continual persuit of efficient methods for their synthesis remains crucial. Traditionally, the preparation of such compounds heavily relied on intricate multi-step syntheses and the use of highly prefunctionalized starting materials. Over the past two decades, the direct sulfuration of C-H bonds has evolved into a straightforward, atom- and step-economical method for the preparation of organosulfur compounds. This review aims to provide an up-to-date discussion on direct C-H disulfuration, dithiocarbamation, xanthylation, thiocarbamation and thiocarbonation, with a special focus on describing scopes and mechanistic aspects. Moreover, the synthetic limitations and applications of some of these methodologies, along with the key unsolved challenges to be addressed in the future are also discussed. The majority of examples covered in this review are accomplished via metal-free, photochemical or electrochemical approaches, which are in alignment with the overraching objectives of green and sustainable chemistry. This comprehensive review aims to consolidate recent advancements, providing valuable insights into the dynamic landscape of efficient and sustainable synthetic strategies for these crucial classes of organosulfur compounds.

Chemo- and Site-Selective Replacement of N-Terminal Carbamates in Peptides

In peptide synthesis, it is important to distinguish the terminal amino group and carry out the selective transformation of only the N-terminal protecting group. We describe herein a reaction for the chemo- and site-selective replacement of carbamates with various other carbamates only at the N-terminus of peptides. We demonstrate the scope of carbamates and peptides and the introduction of fluorine into a peptide. This strategy is applicable to the late stage of peptide synthesis.

New efficient synthesis of tRNA related adenosines bearing the hydantoin ring (ct6A, ms2ct6A) by intramolecular cyclization of N6-(N-Boc-α-aminoacyl)-adenosine derivatives

A novel and efficient way for synthesis of N6-hydantoin modified adenosines, which utilizes readily available N6-(N-Boc-α-aminoacyl)-adenosine derivatives, was developed. The procedure is based on the epimerization free Tf2O-mediated conversion of the Boc group into an isocyanate moiety, followed by intramolecular cyclization. Using this method two recently discovered hydantoin modified tRNA adenosines, i.e. cyclic N6-threonylcarbamoyl-adenosine (ct6A) and 2-methylthio-N6-threonylcarbamoyladenosine (ms2ct6A) were prepared in good yields.

Functionalized Polyhydroquinolines from Amino Acids Using a Key One-Pot Cyclization Cascade and Application to the Synthesis of (±)-Δ7-Mesembrenone

Substituted polyhydroquinolines are ubiquitous skeletal cores found in drugs and bioactive natural products. As a new route to access this motif, we successfully developed a one-pot cyclization cascade with high chemocontrol and diastereoselectivity. The sequence generates two cycles, three carbon-carbon bonds, and an all-carbon quaternary center in a highly convergent process. Functionalized polyhydroquinolines and congeners can be accessed from commercially available amino acids. This versatile and robust strategy was applied to the synthesis of (±)-Δ7-mesembrenone.

Efficient access to 3'-O-phosphoramidite derivatives of tRNA related N 6-threonylcarbamoyladenosine (t6A) and 2-methylthio-N 6-threonylcarbamoyladenosine (ms2t6A)

An efficient method of ureido linkage formation during epimerization-free one-pot synthesis of protected hypermodified N 6-threonylcarbamoyladenosine (t6A) and its 2-SMe analog (ms2t6A) was developed. The method is based on a Tf2O-mediated direct conversion of the N-Boc-protecting group of N-Boc-threonine into the isocyanate derivative, followed by reaction with the N 6 exo-amine function of the sugar protected nucleoside (yield 86-94%). Starting from 2',3',5'-tri-O-acetyl protected adenosine or 2-methylthioadenosine, the corresponding 3'-O-phosphoramidite monomers were obtained in 48% and 42% overall yield (5 step synthesis). In an analogous synthesis, using the 2'-O-(tert-butyldimethylsilyl)-3',5'-O-(di-tert-butylsilylene) protection system at the adenosine ribose moiety, the t6A-phosphoramidite monomer was obtained in a less laborious manner and in a remarkably better yield of 74%.

Simple and efficient synthesis of bicyclic enol-carbamates: access to brabantamides and their analogues

A simple and short synthesis of bicyclic enol-carbamates with high E/Z selectivity and the synthesis of brabantamide A analogue are presented.

One stone two birds: cobalt-catalyzed in situ generation of isocyanates and benzyl alcohols for the synthesis of N-aryl carbamates

An efficient method for the synthesis of N-aryl carbamates from N-Boc-protected amines has been developed. The cobalt-catalyzed in situ generation of isocyanates from N-Boc-protected amines and benzyl alcohols from benzyl formates has been achieved for the first time, which in turn furnished the corresponding benzyl carbamates in moderate to high yields. The reaction was catalyzed by CoI₂ with tris-(4-dimethylaminophenyl)-phosphine as the ligand and zinc powder as the reductant. The developed reaction conditions were found to be compatible for aromatic amines with both electron-donating and -withdrawing substituents.

Metal-Free Catalytic Synthesis of Thiocarbamates Using Sodium Sulfinates as the Sulfur Source

A novel molecular iodine-catalyzed protocol for the construction of thiocarbamates from readily available sodium sulfinates, isocyanides, and water has been described. The present methodology offers a facile and practical route to a variety of thiocarbamates in moderate to good yields with favorable functional group tolerance by use odorless sodium sulfinates as the sulfur source. The mechanistic studies suggest the present transformation involves a radical process.

Direct thiocarbamation of imidazoheterocycles via dual C–H sulfurization

Direct thiocarbamation via dual C–H sulfurization.

Molecular iodine-mediated synthesis of thiocarbamates from thiols, isocyanides and water under metal-free conditions

A simple and practical molecular iodine-mediated method for the efficient construction of thiocarbamates from isocyanides, thiols and water under metal-free and mild conditions has been developed. A variety of thiocarbamates were easily synthesized through this methodology, which has the advantages of simple operation, eco-friendly conditions, good functional group tolerance, and readily accessible raw materials.

Investigation of salicylanilide and 4-chlorophenol-based N-monosubstituted carbamates as potential inhibitors of acetyl- and butyrylcholinesterase

Based on the presence of carbamate moiety, twenty salicylanilide N-monosubstituted carbamates concomitantly with their parent salicylanilides and five newly prepared 4-chlorophenyl carbamates obtained from isocyanates were investigated using Ellman's method for their in vitro inhibitory activity against acetylcholinesterase (AChE) from electric eel and butyrylcholinesterase (BChE) from equine serum. The carbamates and salicylanilides exhibited mostly a moderate inhibition of both cholinesterase enzymes with IC₅₀ values ranging from 5 to 235 µM. IC₅₀ values for AChE were in a narrower concentration range when compared to BChE, but many of the compounds produced a balanced inhibition of both cholinesterases. The derivatives were comparable or superior to rivastigmine for AChE inhibition, but only a few of carbamates also for BChE. Several structure-activity relationships were identified, e.g., N-phenethylcarbamates produce clearly favourable BChE inhibition. The compounds also share convenient physicochemical properties for CNS penetration.

Metal-free direct thiocarbamation of imidazopyridines with carbamoyl chloride and elemental sulfur

Metal-free direct thiocarbamation of imidazopyridines using elemental sulfur.