Sulfuranes. 30. An alkylaryldialkoxysulfurane oxide with labile .alpha. protons. A new kind of pentacoordinated sulfur ylide

Diastereoselective Synthesis of γ‐Lactones through Reaction of Sulfoxonium Ylides, Aldehydes, and Ketenes: Substrate Scope and Mechanistic Studies

“… [25] We hypothesize that the −NMe 2 and O‐enolate substituents of intermediate F occupy apical positions at sulfur (in a trigonal bipyramidal geometry) in transition state J (Scheme 8). Such an arrangement is consistent with those previously reported for cyclic sulfurane oxides bearing electronegative substituents [13–15] . Chelation of the enolate O‐atom (derived from aldehyde) and the N‐atom of the −NMe 2 group by the metal (M=Li or MgCl) would provide important transition state organization for the achievement of high diastereoselectivity (Scheme 8).…”

“…Extensive studies by Martin's group and others have demonstrated that cyclic sulfurane oxides, including optically active examples, can be formed [13,14] . Sulfurane oxide anion E would then be generated through deprotonation of D by a base (e. g. ylide 2 f ), which would subsequently undergo E1cB elimination to give enolate F [15] . We surmise that enolate F undergoes equilibration to the thermodynamically more stable E ‐enolate geometry under the reaction conditions, with final geometry as depicted in Scheme 2.…”

Diastereoselective Reaction of Sulfoxonium Ylides, Aldehydes and Ketenes: An Approach to trans-γ-Lactones

“…Presumably, cyclization of enolate B to give six-membered sulfurane oxide D is faster than formation of lactone C . Many examples of cyclic sulfurane oxides, even optically active ones, are known. , Deprotonation of D by a base (e.g., ylide 2a ) gives sulfurane oxide anion E , which then undergoes E1cB elimination to give enolate F . We propose that enolate F undergoes equilibration to the thermodynamically more stable E -enolate geometry under the reaction conditions (final geometry as depicted in Scheme ).…”

“…Presumably, cyclization of enolate B to give sixmembered sulfurane oxide D is faster than formation of lactone C. Many examples of cyclic sulfurane oxides, even optically active ones, are known. 16,17 Deprotonation of D by a base (e.g., ylide 2a) gives sulfurane oxide anion E, which then undergoes E1cB elimination to give enolate F. 18 We propose that enolate F undergoes equilibration to the thermodynamically more stable E-enolate geometry under the reaction conditions (final geometry as depicted in Scheme 2). Enolate F then undergoes a [3,3]-sigmatropic rearrangement in stereoselective fashion, presumably via a chair transition state, to afford carboxylate G. The latter proposed rearrangement is reminiscent of that observed by Marino and co-workers in the reaction of vinyl sulfoxides with dichloroketene.…”

A new type of σ-sulfurane with a transannular S...N bond: structures of S-substituted N-methyl-6,7-dihydro-5H,12H +-dibenzo[b,g][1,5]thiazocinium salts and N-methyl-6,7-dihydro-5H-dibenzo[b,g][1,5]thiazocine S-oxide

“…For a typical spirosulfurane with two apical No ligands the S-N bond lengths are 1.899 and 1.897 A and the C-S-C angle is 104.8 ° (Adzima et al, 1978). (III) is the first example of a o'-alkylsulfurane with an apical alkyl group, although o--sulfurane with an equatorial methyl group was reported by Lau & Martin (1977). (1) 1037 (4) 1437 (4) 2501 (5) C (2) 328 (4) 1858 (5) 2584 (6) C (3) -116 (5) 1697 (6) 3435 (7) C (4) 141 (5) 1120 (6) 4167 (7) C (5) 846 (5) 676 (6) 4069 (6) C (6) 1309 (4) 843 (5) 3214 (6) C (7) 2070 ( 4844 (8) 7577 (9) 8939 (5) 4-6 C (4) 5569 (8) 6598 (10) 8896 (5) 4-7 C (5) 5331 (7) 5656 (9) 8397 (5) 4.3 C (6) 4307 (7) 5701 (8) 7919 (4) 3-5 C (7) 3978 (7) 4718 (8) 7368 (5) 4.1 C (8) 3782 (7) 6146 (9) 6330 (4) 4.4 C (9) 3039 (6) 7285 (8) 6150 (4) 3.7 C (10) 3076 (8) 7995 (10) 5527 (5) 4.9 C (11) 2392 …”