Synthesis, structure, and reactivity to nucleophiles of 3-benzylidene- and 3-ethylidene-2,3-dihydro-2-methyl-1,2-benzothiazin-4-one 1,1-dioxides

Synthesis and properties of nitrogenous heterocycles containing a spiro-fused cyclopropane fragment

“…The reaction of 3-methylidene-2,3-dihydrothiazin-4-one derivatives 189 containing an enone system with ylides 190 results in spiro[cyclopropanedihydrothiazines] 191. 126 If ylide 190 contains a benzoyl substituent, a mixture (* 1 : 2) of spirocyclopropane and dihydrofuran derivatives 191b,c and 192b,c is formed. Unsaturated ylide 190 (R 2 = H) reacts with the enone 189 (R 1 = Ph) to give only spiro[cyclopropanedihydro-1,2-benzothiazine] 191a.…”

“…Unsaturated ylide 190 (R 2 = H) reacts with the enone 189 (R 1 = Ph) to give only spiro[cyclopropanedihydro-1,2-benzothiazine] 191a. It is believed 126 that the process starts with nucleophilic attack of ylides 190 on the b-carbon atom of the C=C bond in the enones 189; this results in resonance-stabilised betaines, which then undergo cyclisation at the carbon or oxygen atoms to give three-or five-membered rings. The direction of betaine cyclisation is determined by both electronic and steric factors.…”

“…The direction of betaine cyclisation is determined by both electronic and steric factors. 126 A common method for the introduction of the spirocyclopropane fragment in a morpholinone structure is the reaction of their methylidene derivatives 193, which are obtained from the phosphonate 194 using the Wittig reaction, with sulfur ylides. 127 It should be noted that the diastereoselectivity of methylenation of the double bond by the ylide 195 is higher than that by the ylide 190a; diastereomers of spirane derivatives 196a ± f are formed preferentially (or exclusively) in yields higher than 82% (with the exception for compound 196e).…”