Synthesis of sulfur-containing heterocycles via ring enlargement

Abstract

The current review deals with the use of ring expansion reactions for the synthesis of sulfur-containing heterocycles. Ring enlargement offers by far a convenient method for the synthesis of 'medium-sized ring systems', which are usually difficult to obtain or even produced in low yields. These reactions are often catalytically processed starting from a single cyclic precursor and, therefore, are superior to alternative classical iterative synthetic approaches in terms of atomic and conversion efficiency. The current review aims to shed light on the synthetic approaches that exist to afford medium-sized sulfur heterocycles from preexisting smaller rings (e.g., three-, four-, five-, six- and seven-membered rings).

Synthesis, Characterization and Antimicrobial Evaluation of Novel 6’-Amino-spiro[indeno[1,2-b] quinoxaline[1,3]dithiine]-5’-carbonitrile Derivatives

“…1 Sulfur-containing heterocyclic compounds are particularly noteworthy in organic chemistry, medicine, and biochemistry due to their structure. [2][3] Spiro heterocyclic compounds lead to the biological activity of these compounds because of the commonality of a carbon between the two rings and the lack of symmetry of these compounds due to the asymmetric nature of carbon spiro compounds. [4][5][6][7][8] Biological activities, such as promising antibacterial, antifungal, [9][10][11] anti-hyperglycemic, 12 and anti-tubercular 13 effects have been reported for spiro heterocyclic compounds.…”

Rhodium-Catalyzed Ring Expansion Reactions for the Concise Construction of Densely Functionalized Oxathionines and Oxathiocines

“…2c−f Among these rings, sulfur-containing heterocycles are of particular interest due to the unique physiochemical properties of sulfur. 3 However, compared with ubiquitous construction of fiveand sixmembered S-rings, 4 the assembly of medium-sized S-heterocycles is still limited and premature. Therefore, the development of novel and efficient synthetic protocols for the synthesis of such scaffolds is highly desirable in organic and medicinal chemistry.…”

“…6 Recently, a new pathway has emerged as a renaissance of interest in sulfur chemistry 7 due to sulfur's popularity in bioactive molecules and organic materials. 8 Via this novel [1,4]-acyl rearrangement, 7−10-membered rings can be prepared (Figure 1a). 9 The formation of C(sp 2 )−S bond was a complementary feature, as the former process always constructed the C(sp 3 )−S bond.…”

“…Herein, we report the ring expansion of thiochromenes and aromatic thiophenes to assemble functionalized oxathionines and oxathiocines via rhodium catalysis (Figure 1c). We assume that the formation of the medium-sized product starts with the Finally, the medium-sized ring product can be obtained through a [1,4]-sigmatropic rearrangement process. The preliminary investigation was conducted using benzothiochromene 2a and 1-diazonaphthoquinone (1-DNQ) 1a in toluene at 40 °C.…”

Formation of Tetrahydrothiophenes via a Thia-Paternò–Büchi-Initiated Domino Photochemical Reaction

“…The light-initiated Paternò–Büchi reaction, which combines a photochemically excited carbonyl compound with an alkene to give the oxetane, is a well-developed and synthetically useful process for which many successful applications are described in the literature. , In stark contrast, a very limited number of photochemical reactions of a thiocarbonyl compound with an alkene to give a thietane, the so-called thia-Paternò–Büchi reaction, have been described in the literature, and for the most part these studies date from several decades ago . It appeared to us that this reaction had been underexploited for the preparation of sulfur-containing four-membered ring compounds, which are high-value intermediates in organic synthesis for post-functionalization, such as in ring enlargement or ring opening reactions . We therefore undertook a reinvestigation of the thia-Paternò–Büchi reaction between thiobenzophenone derivatives and alkene partners, and in the course of this study we discovered an unprecedented thia-Paternò–Büchi-initiated domino photochemical reaction, as we disclose below.…”