Synthesis of Functionalized Arenopyrans and Arenylsulfanes by Reacting Nitroallylic Acetates with Arenols and Arenethiols

Abstract

Nitroallylic acetates react with naphthols and electron‐rich phenols under mild conditions (TEA, DCM, room temp.) to afford arenopyrans in moderate to excellent yields. Such (3+3) annulation of a 1,3‐bielectrophilic nitroallylic acetate and a 1,3‐binucleophilic arenol involving an SN2′ reaction and an intramolecular 6‐endo‐trig cyclization takes place in a regio‐ and stereoselective manner. Surprisingly, the reaction of arenethiols under the same conditions provided nitroallylic thioethers instead of the expected arenothiopyrans presumably through a direct SN2 reaction.

Metal and Oxidant-Free Brønsted Acid-Mediated Cascade Reaction to Substituted Benzofurans

“…To favor cyclization, 4- tert -butyl- and 4-benzyl-phenols 4d,e , blocked in the para position, were tested obtaining the corresponding benzofurans 6a,b but only in 13 and 19% yields (Table ). A different behavior was observed when the 2-naphthol 4f was employed as the starting material: the electronic features of the polycyclic system enhanced the nucleophilicity of the sp 2 carbon in position one and the corresponding naphtho­[2,1- b ]­furan-1-carboxylates 6c–e were obtained in good yields (68–74%, Table ).…”

Recent advances in the synthetic applications of Morita–Baylis–Hillman and Rauhut–Currier adducts of nitroalkenes

“…In 2018, our group reported the reactivity difference of phenols/naphthols 53 and arenethiols 54 towards the primary MBH acetates of nitroalkenes 33 (Scheme 17). 27 Naphthols and electron-rich phenols 53 reacted with MBH acetates 33 via an S N 2′ reaction followed by intramolecular oxa-Michael addition to form substituted arenopyran derivatives 55 and 56 . The MBH acetates 33 possessing electron-donating substituents on the aryl ring afforded the products in good yields; however, substrates with electron-withdrawing substituents did not afford the expected products.…”

Synthesis of tetrahydrochromenes and dihydronaphthofurans via a cascade process of [3 + 3] and [3 + 2] annulation reactions: mechanistic insight for 6-endo-trig and 5-exo-trig cyclisation

“…The reaction with reduced base equivalents led to reduced yields concluded that 2.0 equiv. of Cs 2 CO 3 is desirable to yield tetrahydrochromene 3a under the present reaction conditions (Table 1, entries [9][10][11]. Further, increase of Cs 2 CO 3 with 3.0 equiv.…”

“… 1 A few molecules synthesized using nitro allylic acetates have shown promising cytotoxic, trypanocidal and AchE inhibition 2 activity in pharmaceutical and medicinal chemistry. Nitro allylic MBH acetates have been used as main precursors in organocatalysis 3 and heterocyclic chemistry, 4 and as bicyclic skeletons 5 for the construction of elegant building blocks like tetrahydro-pyranoquinolinones, 6 sulfonyl furans, 7 pyranonaphthoquinones, 8 arenopyrans/arenylsulfanes, 9 triazoles, 10 a tetrasubstituted furans, 10 b fused furans, 10 c , d tetrasubstituted pyrroles, 11 a benzofuranones, 11 b and tetrahydropyrano scaffolds/pyranocoumarins. 12 The nitro allylic MBH-acetates can also undergo asymmetric benzylic 13 a and allylic alkylation 13 b reactions as well as kinetic resolution [KR] 13 c , d under normal conditions.…”