Synthesis and Stereochemistry of Saturated and Partially Saturated 4‐Aryl‐4H‐3,1‐benzothiazine‐2(1H)‐thiones

Abstract

The reaction of 2‐arylidenecyclohexanones 1 with dithiocarbamic acid gave three of the four possible diastereomers of 4‐aryl‐4a,5,6,7,8,8a‐hexahydro‐8a‐hydroxy‐4H‐3,1‐benzothiazine‐2(1H)‐thiones 2–4. The isomeric composition of the reaction products was found to depend on the quantity of hydrochloric acid used as catalyst. 1H‐NMR studies showed that the preferred conformation of the cis isomers 2 and 4 is controlled by the bulky 4‐aryl group, which always occupies the energetically more favourable quasiequatorial position. Dehydration of 2–4 afforded the corresponding 4‐aryl‐tetrahydro‐4H‐3,1‐benzothiazine‐2(1H)‐thiones 5 and 6. The orientation of the dehydration reactions depends on the configuration of the starting compounds 2–4 and the reaction conditions used.

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“…X-ray analysis of the compound showed the cyclopentane and the 1,3-thiazine rings being cisfused and the 4-phenyl group in trans position to the annelated H-4a atom [13]. These results can be explained by trans-addition of dithiocarbamic acid onto the polarized carbon-carbon double bound followed by a conformation-driven cyclization of the open-chain adduct [9]. The stereochemistry of the isolated adduct is the same as that of obtained in similar reaction of (E)-2-benzylidenecyclohexanone under less acidic conditions [8,9].…”

“…It was found that the reaction results in formation either open-chain or cyclic adducts depending on the substitution pattern of the aromatic rings of the chalcones [6]. Later, we have reported on stereochemical analysis of reactions with dithiocarbamic acid of (E)-2-benzylidenecyclohexanones [8,9] and some (E)-2-benzylidene-1-benzocylanones [10]. Reactions of the investigated compounds led to formation of cyclic [8,9] or open chain [10] adducts.…”

“…Later, we have reported on stereochemical analysis of reactions with dithiocarbamic acid of (E)-2-benzylidenecyclohexanones [8,9] and some (E)-2-benzylidene-1-benzocylanones [10]. Reactions of the investigated compounds led to formation of cyclic [8,9] or open chain [10] adducts. Stereochemistry of the formed adducts were found to be determined by both the structure of the α,b-unsaturated carbonyls and the reaction conditions.…”

“…Stereochemistry of the formed adducts were found to be determined by both the structure of the α,b-unsaturated carbonyls and the reaction conditions. Addition reaction with dithiocarbamic acid of (E)-2-benzyldenecylohexanones resulted in formation of isomeric cyclic adducts [8,9]. In such a case three new chiral centers are formed allowing formation of four diastereomeric pairs.…”

“…In the reactions formation of three of the possible diastereomers could be detected and characterized. Stereochemistry of cyclization of the primary (Michael-type) adducts was determined by the preferred conformation of the forming bicyclic saturated heterocycles [8,9]. The aim of the present work is to investigate the structure and stereochemistry of the dithiocarbamic acid adducts of the fivemembered analogue (E)-2-arylidenecyclopentanones (1a-c).…”