5- Aminosulfoxonium salts

The methylation of sulfoximines 45 with Me30BF4 proceeded readily and gave the corresponding cyclic aminosulfoxonium salts 46 in quantitative yields. Upon treatment with LiN(H)t-Bu first at-78 °C and then at room temperature, salts 46 delivered the enantio- and diastereomerically pure bicyclic 2,3-dihydrofurans 50 cleanly in high overall yields. It is proposed that the reactions of the aminosulfoxonium salts 40 and 46 with the lithium amide at low temperatures afford the vinyl aminosulfoxonium ylides 41 and 47, respectively. These alkylidene carbenoids eliminate sulfinamide 35 at higher temperatures with formation of the alkylidene carbenes 42 and 48, respectively. Subsequently, the alkylidene... 

The ready deprotonation of the vinyl aminosulfoxonium salts 46 with a strong base at the a-position prompted a study of their reactions with weaker bases. It was speculated that in this case a vinyl-allyl isomerization of 46 might occur, followed by an intramolecular substitution of the allyl aminosulfoxonium salt... 

Tetrahydrofurans 53 should be of synthetic interest because of the many natural products containing a bicyclic tetrahydrofuranoid skeleton or structural element [30]. The double bond would allow further synthetic transformations. While the chances of a regioselective isomerization of 46 to the allyl aminosulfoxonium salts 52 seemed to be good, the prospects of a cyclization of the latter with formation of 53 were considered to be less promising because of the poor nucleophilicity of the silyloxy group. 

Scheme 1.3.20 Asymmetric synthesis of unsaturated bicyclic tetrahydrofurans via intramolecular substitution of allyl aminosulfoxonium salts.

The acyclic sulfonimidoyl-substituted amino acids 24 were selected as starting material for the synthesis of the unsaturated prolines of type 63. Because of the facile synthesis of the unsaturated bicyclic tetrahydrofurans 53 from the vinyl aminosulfoxonium salts 46 (cf. Scheme 1.3.20), it was speculated that upon treatment with a base the vinyl aminosulfoxonium salts 67 would experience a similar isomerization with formation of the allyl aminosulfoxonium salts 69, which in turn could suffer an intramolecular substitution of the allylic aminosulfoxonium group (Scheme 1.3.24). The methylation of sulfoximines 24 with Me30Bp4 gave... 

When acyclic and cyclicl-alkenyl aminosulfoxonium salts were allowed to react with a base, p-silyloxy alkylidene carbenes were generated, which underwent a l,5-0,Si-bond insertion and 1,2-silyl migration to form 2,3-dihydrofurans <04JA485ft>. As can be seen in the scheme below, 2,3-dihydrofurans could also be formed from various 2,2-dimethyl-5-methoxy-carbonyloxy-3-pentyn-l-ols in the presence of p-methoxyphenol via a palladium-catalyzed cyclization reaction <04TL1861>. 

S-Aminosulfoxonium salts Sulfinic acid amides Sulfoximines Thionylimines... 

Reactions with S-aminosulfoxonium salts via their ylids Ring closures... 

Mesitylenesulfonyloxylamine has been used for N- and S-aminations, e. g. the preparation of S-aminosulfoxonium salts from sulfoxides... 

Alkylthio-l-oximes S-Aminosulfoxonium ylids 1-Imino-l-sulfenic acids Oxathiol-2-ylidenimmonium salts... 

Acylaminosulfenium salts S-Acylhydrosulfamines N-Acylsulfenamides N-Acylsulfilimines 1 - Alkoxy-1 -alkylthio-1 -amines 1 - Alkylthio-1 -oximes S-Aminosulfoxonium ylids Carboxylic acid thioamide S-oxides... 

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