First thia-Diels–Alder reactions of thiochalcones with 1,4-quinones

Abstract

Aryl and hetaryl thiochalcones react smoothly with 1,4-quinones in THF solution at 60 °C yielding the corresponding fused 4H-thiopyrans after spontaneous dehydrogenation of the initially formed [4 + 2] cycloadducts. In general, the yields of the isolated products were high. With 5-chloro-10-hydroxy-1,4-anthraquinone, the thia-Diels–Alder reaction occurred with complete regioselectivity. In the case of the reaction of vitamin K3 (menadione) with diphenylthiochalcone, the initial cycloadduct was isolated in 37% yield.

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

“…In addition, an important issue of the work was the examination of the chemoselectivity governing the formation of five-membered rings via competitive cycloaddition of the in-situ-generated 1,3-dipoles either onto the C=C or C=O bond. The present work should also be considered as an extension of our earlier studies focused on the exploration of 1,4-quinones in the [3 + 2]-cycloaddition and hetero-Diels–Alder reaction performed with thiocarbonyl S -methanides and thiochalcones, respectively [ 37 – 38 ].…”

Recent Developments on the Synthesis of Various Sulfur‐Containing Heterocycles via [3+2]‐ and [4+2]‐Cycloaddition Reactions with Thiocarbonyls

“…Heimgartner and co‐workers reported another thia‐Diels‐Alder reaction of thiochalcone as heterodiene ( 86 ) with 1,4‐quinones ( 87 , Scheme ). Initially formed cycloadducts ( 88 ) underwent rapid oxidation to compounds 89 .…”

The [4+2]‐Cycloaddition of α‐Nitrosoalkenes with Thiochalcones as a Prototype of Periselective Hetero‐Diels–Alder Reactions—Experimental and Computational Studies

“…All compounds were prepared according to a known procedure based on the treatment of the corresponding chalcones 12 with Lawesson's reagent (LR) (Scheme 3). [16] The "thiochalcone fractions" containing predominantly mixtures of dimers 2 and 4 were isolated chromatographically and subsequently used for further studies without separation of the components. In analogy to earlier reports, [13b,c] compounds bearing phenyl (1 a-g) or ferrocenyl (1 h, i) groups located at the C=S group (Ar 1 ) provided complex mixtures of dimers 2 and 4, and depending on the type of substituents, the composition of the mixtures slightly differed in the studied cases.…”

“…In contrast, in our recent publication, organocatalytic asymmetric [4+2]‐cycloadditions of thiochalcones 1 as heterodienes with in situ generated enantiopure dienamines derived from O‐silylated l ‐prolinols have also been demonstrated . In addition, we described thia‐Diels–Alder reactions of 1 acting as heterodienes with acetylenic dienophiles as well as with 1,4‐quinones . Notably, in the case of unsymmetrically activated acetylenes such as 8 , the [4+2]‐cycloadditions occurred with complete regioselectivity, and the sulfur atom attacked always the β‐position of the Michael‐type acceptor to give 4 H ‐thiopyrans 9 (Scheme ) .…”