Synlett

A palladium-catalyzed cycloisomerization of carbamimidothioates with the formation of a quaternary carbon and a sulfide is described. The use of (IPr)Pd(allyl)Cl (CX21), K3PO4, and Me-C(OTBS)=NTBS in refluxing xylenes was optimal, and the methoxycarbonyl group was the most suitable substituent for the nitrogen atom of the carbamimidothioate. Phenyl and alkyl groups can be used as tethers for carbamimidothioates, and alkyl and aryl carbamimidothioates can undergo Pd-catalyzed cycloisomerization in high yields.

Pyrylium salts based on a cationic oxygen heterocycle are a key class of chromophores. However, synthesis of these salts generally requires use of harsh acids, copious organic solvents, and in many cases, hazardous conditions. This work provides a two-pot synthesis for substituted triphenyl pyrylium salts wherein chalcone intermediates are first prepared and then mild methanesulfonic acid is used in combination with a dehydrating agent to drive pyrylium cyclization. Purification is achieved through a simple, aqueous workup involving counterion metathesis which avoids the need for environmentally unfriendly organic solvents. This mild, green approach has been applied to synthesize a collection of known pyryliums as well as a new family of red-shifted pyrylium chromophores bearing p-pyrrolidinylphenyl substituents. The synthesis of the latter group demonstrates that unlike other current methods, our approach offers enhanced functional group tolerance as well as finer control over substituent placement.

Since the pioneering work by Grignard in 1900, organomagnesium reagents, the so-called Grignard reagents, have been indispensable in organic synthesis. Alkyl Grignard reagents are usually prepared from the corresponding alkyl iodides, bromides, or chlorides with Mg, whereas alkyl fluorides are not viable substrates under conventional conditions due to the high stability of the C–F bonds. We report that Al–Rh bimetallic complexes catalyze the magnesiation of C(sp3)–F bonds of alkyl fluorides using easy-to-handle Mg powder. The present conditions can accommodate primary, secondary, or tertiary alkyl fluorides to afford the corresponding alkylmagnesium reagents, which can be successfully converted into various functionalities.

Baclofen is an active pharmaceutical ingredient used for the treatment of muscle spasticity. We describe our efforts to develop a novel synthetic approach through C–C bond formation and a cost-effective route to baclofen. The synthesis involved a two-step approach through C–C bond formation using the extensively and commercially available starting material 4-chlorobenzyl cyanide with chloroacetic acid as a reagent in an aprotic solvent, followed by reduction of the nitrile functional group. The synthetic route to baclofen has been demonstrated to be commercially viable, cost-effective, and environmentally friendly. Execution of the developed process led to the isolation of (+)-baclofen in an overall yield of 60% at a multikilogram scale with >99.5% HPLC purity. This article also discusses the cost-effectiveness of the process, the impurity profiling, and the product quality.

A photooxidation approach to the conversion of phosphines into the corresponding phosphine oxides is reported. By taking advantage of O2 in the air as an oxidant and oxygen source, phosphine oxides were obtained efficiently in moderate to excellent yields. A four-coordinated organoboron compound was used as the photocatalyst to activate O2 to its singlet state. This photooxidation method features mild reaction conditions, broad functional-group tolerance, and a wide substrate scope.

Synlett 2024; 35: VIII-DOI: 10.1055/s-0043-1763678Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

Synlett 2024; 35: A22-A35DOI: 10.1055/s-0040-1720622Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

Synlett 2024; 35: III-IIIDOI: 10.1055/s-0043-1763677Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

A metallaphotoredox-catalyzed synthesis of heterodiarylmethanes using mild reaction conditions, commercially available substrates, and bench-stable catalysts is demonstrated. Moderate yields are obtained, and further derivatization of the newly formed benzylic position is shown.

The selective functionalization of 1,3-bis(boronic) esters holds the potential for creating diverse molecular structures, particularly through the late-stage functionalization of the remaining C–B bond. By employing distinct organometallic reagents, we have developed a method for regiodivergent alkynylation of 1,3-bis(boronic) esters, facilitated by unique chelation patterns. Notably, this methodology effectively overcomes limitations commonly encountered in radical chemistry, which generates only monoselective downstream targets. Furthermore, the compounds synthesized through this approach can serve as significant building blocks, contributing to the construction of molecular complexity.