Synthesis of 2<i>H</i>-1,2-Benzothiazine 1,1-Dioxides via
Heteroannulation Reactions of 2-Iodobenzenesulfonamide with
Ketone Enolates under S<sub>RN</sub>1 Conditions<sup>§</sup>
William J. Layman,
Thomas D. Greenwood
Aaron L. Downey
James F. Wolfe
10.1021/jo050964e.s001
https://acs.figshare.com/articles/dataset/Synthesis_of_2_i_H_i_1_2_Benzothiazine_1_1_Dioxides_via_Heteroannulation_Reactions_of_2_Iodobenzenesulfonamide_with_Ketone_Enolates_under_S_sub_RN_sub_1_Conditions_sup_sup_/3257629
2-Iodobenzenesulfonamide (<b>1a</b>) underwent photostimulated S<sub>RN</sub>1 reactions in liquid NH<sub>3</sub> with the
potassium enolates derived from acetone, pinacolone, butanone, and 3-methyl-2-butanone to give
fair to good yields of 2<i>H</i>-1,2-benzothiazine 1,1-dioxides<b> 2</b>. Reductive dehalogenation of <b>1a </b>was found
to predominate in photoinduced reactions of <b>1a</b> with 3-pentanone, 2-methyl-3-pentanone, and 2,4-dimethyl-3-pentanone, the extent of reduction being proportional to the number of β-hydrogen atoms
present in the ketone enolate. Isotopic labeling studies with 2,4-dimethyl-3-pentanone-<i>d</i><sub>14</sub> (<b>24</b>)
confirmed the major role of the β-hydrogens in the reduction process. Reactions of<b> 1a</b> with
cyclopentanone, cyclohexanone, and cyclooctanone enolates afforded new tricyclic benzothiazine
derivatives <b>26</b>−<b>29</b>. Attempts to extend the heteroannulation reaction to the preparation of 2<i>H</i>-1,2-benzothiazin-3(4<i>H</i>)-one 1,1-dioxides <b>3</b> (R = H, Ph) through reactions of <b>1a</b> with <i>tert</i>-butyl acetate
and ethyl phenylacetate enolates resulted only in hydrodehalogenation of <b>1a</b>. However, oxazoline
anion<b> 30</b>, a synthetic equivalent of ethyl phenylacetate, was successfully employed in an alternative
S<sub>RN</sub>1-based synthesis of benzothiazine <b>3</b> (R = Ph).
2005-11-11 00:00:00
heteroannulation reaction
butyl acetate
methyl
Ketone Enolates
ketone enolate
ethyl phenylacetate
Ph
Heteroannulation Reactions
dioxide
photostimulated S RN 1 reactions
Reductive dehalogenation
benzothiazine 3
NH 3
dimethyl
ethyl phenylacetate enolates
reduction process
Iodobenzenesulfonamide
photoinduced reactions
potassium enolates
oxazoline anion 30
cyclooctanone enolates