Alkenyl sulfonate

Giblin, G.M.P., Jones, C.D., Simpkins, N.S. (1997) A Concise Stereoselective Synthesis of Epi-batidine Employing Conjugate Addition to an Alkenyl Sulfone Intermediate as the Key Step. Syniett, 589-590. 

Denmark and Harmata studied the reaction of 1,2-allenyl sulfones and 2-prope-nols under the catalysis of 5 mol% of sodium alkoxide affording 2-alloxy-2-propenyl sulfone 217, which can be converted to 2-oxo-5-alkenyl sulfone 218 by treatment with 1.5equiv. of KH in HMPA, a carbanion-accelerated Claisen rearrangement [116, 117]. 

The reaction of 1,2-allenyl sulfones with EtOH in the presence of a catalytic amount of EtOK afforded 2-ethoxy-2-alkenyl sulfones 221, which can be easily alky-... 

The reaction of PhS02 with 2-(2 -phenylsulfonyl)-2, 3 -butadienylmalonate 233 affords the five-membered cyclic alkenyl sulfone 235 via a 1,4-addition, intramolecular deprotonation and a SN2 -substitution process [124, 125]. 

Scheme 3.23 Rhodium-catalyzed c/ne-substitution of alkenyl sulfones with aryltitanium reagents [41].

Reduction of a,P-unsaturated sulfones.1 Sodium amalgam (7, 326-327) is not satisfactory for reductive cleavage of alkenyl sulfones, R CH=CR2S02C6H5. These substrates are best reduced to alkcncs wth potassium-graphite (65-85% yields). 

Z)-A3-Alkenyl sulfones. The 7r-allylpalladium complexes of 1,3-dienes react with sodium neophylsulflnate to give a palladium complex which on treatment with dimethylglyoxime gives (Z)-sulfones with high regio- and stereoselectivity.3 Example ... 

Moreover, functionalized arylcopper reagents have been reported as appropriate nucleophiles with alkenyl and dienyl sulfonates (Table 5.3, entries 14—18) [18]. Although aryl sulfonates showed little reactivity towards arylcopper reagents, alkenyl sulfonates proved to be much more reactive under the described reaction conditions. 

Table 5.3 Iron catalyzed cross-coupling reactions of alkenyl sulfonates.

Alkenyl sulfones were also identified as suitable substrates by Julia and coworkers, but reduction and 1,4-addition were observed in notable quantities [19]. In some examples, sulfone electrophiles can give good yields and high stereoselectivities (Scheme 5.4). 

Scheme 5.4 Iron-catalyzed cross-coupling reaction of alkenyl sulfones developed by Julia and coworkers.

The classical Julia Olefmation with sodium amalgam might possibly proceed via an initial elimination to an alkenyl sulfone, which would then undergo homolytic cleavage involving single electron transfer. 

The last step of the Julia-Lythgoe olefination is an elimination, which is typically performed with sodium amalgam and starts with an Elcb elimination to give an alkenyl sulfone (mechanistic analysis Figure 4.40) with its reduction to the alkene following in situ. Both the related mechanism and an explanation of the resulting fraws-selectivity will be outlined later in Figure 17.85. 

The reduction of sulfones with Sml2 can result in deoxygenation, to give the parent sulfide,59 or carbon-sulfur bond cleavage, depending on the substrate and the reaction conditions employed.60 For example, alkyl and alkenyl phenyl sulfones are reductively cleaved by Sml2 in the presence of HMPA. In the reduction of alkenyl sulfones, competing reduction of the electron-deficient alkene is not observed (Scheme 4.50).60... 

Alternatively, the classical Julia alkenation of acetoxy sulfones C with sodium amalgam in MeOH might possibly proceed via an initial formation of an alkenyl sulfone F, which would then undergo homolytic cleavage involving single electron transfer (Scheme 4.34). This mechanism is proposed on the basis of deuterium incorporation studies performed by Keck et al . ... 

The examples shown in Scheme 16, which are representative for all other sulfinates studied, demonstrate a high level of stereoselectivity (around 80-90% of the original enantiomeric excess is retained after switching the stereogenic atom from sulfur to carbon). Despite these encouraging results, the somewhat tedious and stereochemically unreliable preparation of the starting sulfinates [47] may be the reason for the reluctance of the chemical community to use this chemistry as an entry to enantiomerically pure 2-alkenyl sulfones. 

Only primary alkyl-metal reagents have been used in these cases, except in the instance of the Fe-cata-lyzed coupling of alkenyl sulfones. 

Epoxysulfones (59) are obtained by epoxidation of alkenyl sulfones (60) (Scheme 28). 

Magnesium. 13, 170 IS, 194 16, 19 Desulfonylation. Various sulf These include alkenyl sulfones. (p-toluenesulfonhydrazides, V-tos la electron-withdrawing group, ring cl precedence to detosylation. ... 

A major drawback when reducing alkenyl sulfones with Na/Hg is that the configuration of the double bond is not necessarily preserved. Additionally, reduction of the double bond is occasionally observed as shown in Eq. 84, where a Julia-Lythgoe olefination process is also taking place.135... 

---