Sulfur ylides Michael addition

Nitronates (5) can be synthesized by the Michael addition of in situ generated sulfur or selenium ylides (12) (58-60, 62, 63) to conjugated nitroalkenes... 

The chemical behavior of heteroatom-substituted vinylcarbene complexes is similar to that of a,(3-unsaturated carbonyl compounds (Figure 2.17) [206]. It is possible to perform Michael additions [217,230], 1,4-addition of cuprates [151], additions of nucleophilic radicals [231], 1,3-dipolar cycloadditions [232,233], inter-[234-241] or intramolecular [220,242] Diels-Alder reactions, as well as Simmons-Smith- [243], sulfur ylide- [244] or diazomethane-mediated [151] cyclopropanati-ons of the vinylcarbene C-C double bond. The treatment of arylcarbene complexes with organolithium reagents ean lead via conjugate addition to substituted 1,4-cyclohexadien-6-ylidene complexes [245]. 

A limited number of other anionic species have been employed as Michael donors in tandem vicinal difunctionalizations. In a manner similar to sulfur ylides described above, phosphonium ylides can be used as cyclopropanating reagents by means of a conjugate addition-a-intramolecular alkylation sequence. Phosphonium ylides have been used with greater frequency261-263 than sulfur ylides and display little steric sensitivity.264 Phosphorus-stabilized allylic anions can display regiospecific 7-1,4-addition when used as Michael donors.265... 

Alkenes susceptible to Michael additions react with sulfur ylides to form cyclopropanes. Examples of typical ylides used in the cyclopropanation reaction of Michael acceptors are presented in Scheme 4. Best results were obtained with stabilized ylides, i.e. ylides of type C, D or E, and yields were enhanced with increase of the electron-withdrawing capacity of the anion stabilizing group in the alkene. The mechanism of the cyclopropanation reaction (Scheme 5) is known, and proceeds in a nonstereospecific manner. The E/Z geometry of the alkene is frequently retained in the product and a high degree of asymmetric induction can be achieved with optically active Michael acceptors or ylides. 

The synthesis of aziridines from imines and sulfur ylides has been reviewed in previous editions of PHC and is a well-known reaction. A current study reveals that telluronium ylides add to a,p-unsaturated imines through a Michael addition-elimination to the olefin followed by a second equivalent of telluronium ylide addition to the imine, which subsequently eliminates to form aziridines 137 and 138 in a ratio of 13 1 <05JA12222>. 

Sulfur ylides are useful as nucleophilic alkylidene transfer agents in reactions with electron-deficient functional groups, forming epoxides with carbonyls, and either undergoing carbonyl addition with epoxide formation or conjugate addition with cyclopropanation with Michael acceptors, depending on the structure of the Michael acceptor [113]. 

The Michael addition of sulfur ylides to nittoalkenes, catalysed by various thioureas, has been studied theoretically. ... 

Tang and co-workers report a catalytic asymmetric cyclopropanation method where the sulfide reacts with an activated alkyl bromide to afford the sulfonium intermediate [163], This is deprotonated by base to generate the sulfur ylide that reacts with electrondeficient alkenes via Michael-addition and S -attack of the enolate formed to give the cyclopropane and to regenerate the sulfide (alkylation-deprotonation. Scheme 7.35). 

Formation of three-membered-ring systems can also be the result of a nucleophilic addition leading to a zwitterionic intermediate, followed by loss of nitrogen. In these cases, the reactions are related to the addition of sulfur or phosphorus ylides to Michael acceptors. ... 

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