Sulfonium salts reaction with base

In an attempt to prepare sulfonium-ylide polymer, Tani-moto and coworkers [57,58] carried out the reaction of a sulfonium salt polymer with benzaldehyde in the presence of a base and obtained styrene oxide. The reaction was considered to process via a ylide polymer formation (Scheme 24), which may be unstable and has not been isolated. 

Sulfur ylides are a classic reagent for the conversion of carbonyl compounds to epoxides. Chiral camphor-derived sulfur ylides have been used in the enantioselective synthesis of epoxy-amides <06JA2105>. Reaction of sulfonium salt 12 with an aldehyde and base provides the epoxide 13 in generally excellent yields. While the yield of the reaction was quite good across a variety of R groups, the enantioselectivity was variable. For example benzaldehyde provides 13 (R = Ph) in 97% ee while isobutyraldehyde provides 13 (R = i-Pr) with only 10% ee. These epoxy amides could be converted to a number of epoxide-opened... 

Such a reaction may occur on treatment of the benzo-fused bicyclic sulfonium salt 37 with various bases under aerobic conditions. The incipient allylic diradical 39 is trapped as 1,3-diradical by molecular oxygen to give a mixture of up to 35% diastereomeric Spiro-1,2-dioxolanes 40. The spirocyclopentene 41 is obtained in a competing path in which allylic diradical 39 is cyclized as a 1,5-carbon-centered diradicaE . 

The alkylidenecarbene generated from alkenyl(phenyl)iodonium tetrafluoroborate by base adds irreversibly to THT to form a sulfonium ylide, which further gives the sulfonium salt along with a small amount of a thioether (Scheme 40). This was in contrast to the corresponding oxonium ylide where the reaction was found to be reversible <1996JA10141>. 

The last, and probably most interesting, example of the approach towards chiral products derived from ylidic 3,2-rearrangements, involves the generation of a chiral ylide by enamioselective deprotonation of a prochiral sulfonium (ammonium) salt using a chiral base. Few attempts have been reported so far, the most noteworthy coming from the laboratory of Trost and involving the reaction of the sulfonium salt (321) with the chiral base (322 Scheme 81). The asymmetric induction is rather poor and represents the extent of prochiral recognition by the chiral base. 

The first synthesis of racemic LTA4 methyl ester, as a mixture with its cis isomer, was reported by Corey et al. as outlined in Scheme 3.19. Alcohol 45 was used as the synthon for the C-12 portion of the target structure and ( , )-2,4-hexadien-l,6-diol became C-6 to C-11. The functionality in the diol was differentiated by its transformation to 47, which then underwent a Wittig reaction with 46 to yield the 15-carbon alcohol 48. The formation of the mesylate of 48 and the reaction of sulfonium salt 49 with methyl 4-formylbutyrate using LDA as a base is also a difficult step and only modest yields of the target compounds are obtained. ... 

Aik 1 hstituted sulfonium salts react with carbonyl compounds in the presence of base to hstituted furans. The first step in this reaction is an alkynyl-allenyl isomerization cheik 24) <73JCS(Pl)65, 90H(31)1003, 93JOC3960). 

In analogy to the properties of ordinary sulfonium salts, reaction of disulfonium dications with bases may lead to either a- or p-deprotonation. Deprotonation of the S-S dication formed during the Pummerer rearrangement of monosulfoxides of certain bis-sulfides 13, 59, 56 is a key step of the overall process. Furukawa and co-workers " also suggested that direct formation of disulfonium dication ylides occurred upon treatment of sulfinyli-mines of 14 and 41 with potassium tert-butoxide. Reaction of triflic anhydride with sulfoxide 100 affords sulfonium salt 102 through deprotonation of the corresponding S-S dication 101 (Scheme 39). ... 

Phosphorus Nucleophiles. Triphenylphosphine is an effective nucleophile for reacting with the bridged sulfonium ion in high yield. The phosphonium salts generated eliminate MeSH upon reaction with base, such as l,8-diazabicyclo[5.4.0]undec-7-ene, resulting in a synthesis of vinylphosphonium salts. If NaOH is used, a vinylphosphine oxide is generated. 

The sulfide 23 was prepared from 21 via 22 in a two step process. Alkylation of 23 with methyl iodide afforded the sulfonium salt 24, which underwent Stevens rearrangement upon reaction with base to give the ferrocenophane 25. Oxidation of 25 followed by elimination gave the strained ethene bridged ferrocenophane 26. 

Several variations of the Feist-Benary reaction furnish substituted furans as products. The following three examples provide synthetically useful alternatives to the standard reaction conditions. One method is based on the reaction of a sulfonium salt with a P-dicarbonyl compound. For example, reaction of acetylacetone (39) with sulfonium salt 38 in the presence of sodium ethoxide yields 81% of trisubstituted furan 40. This strategy provides a flexible method for the preparation of 2,3,4-trisubstituted furans. 

Sulfonium ylides generated through base-promoted deprotonation of sulfonium salt have been extensively studied. The reaction of sulfides with a diazo carbonyl compound in the presence of a transition metal catalyst is an alternative approach to obtain sulfonium ylides. Sulfonium ylides are more stable than the corresponding oxonium ylides. Stable sulfonium ylides generated by the reaction of an Rh(ii) carbene complex with thiophene have been reported (Figure 5). ... 

The reaction of 1,3-dibromopropane with methyl methylsulfanylmethyl sulfoxide in the presence of base gave cyclobutanone via the intermediate formation of ftve-membered cyclic sulfonium salt 6, which was finally converted to 1-methylsulfinyl-l-methylsulfanylcyclobutane (7 a) by a Stevens-type rearrangement in 70% yield which on acid hydrolysis gave cyclo-butanone.142... 

The simplest sulfur ylids are formed from sulfonium salts 69 by deprotonation in base. These ylids react with carbonyl compounds to give epoxides.18 Nucleophilic attack on the carbonyl group 70 is followed by elimination 71 of dimethylsulfide 72 and formation of the epoxide 73. You should compare diagram 71 with diagram 23 in chapter 15. The phosphonium ylid reacted by formation of a P-0 bond and an alkene in the Wittig reaction. The sulfonium compound reacts by formation of a C-O bond 71 as the S-O bond is much weaker than the P-0 bond. The sulfonium salt 69 can be reformed by reaction of 72 with Mel. 

The alcohol has been a spectator of these events so far but the chlorosulfonium ion now formed can react with it to give a new sulfonium salt. This is the sole purpose of all the reactions as this new sulfonium salt is stable enough to survive and to be deprotonated by the base (Et3N). You will recognize the final step both as the redox step and as a close relative to events in the preceding sections. 

A new approach to the synthesis of annulated sulfur heterocycles based on triflic anhydride-promoted electrophilic cyclization of the hetaryl-containing alkyl sulfides, including 1409, was elaborated <2003S1191>. The proposed method includes intermediate formation of sulfonylsulfonium salts 1410 followed by electrophilic attack on the aromatic ring (Scheme 271). Smooth demethylation of initially formed cyclic sulfonium salts 1411 by treatment with EtsN afforded a number of five- 1412 and six- 1413 membered fused sulfur heterocycles. Unexpected ring opening with formation of compound 1414 took place in the reaction of diethylamine with five-membered sulfonium salt 1411. 

Sulfonium salts react in several ways. They may behave as a leaving group, undergoing substitution by a nucleophile or fragmenting with the formation of an alkene. However, the most important reaction of sulfonium salts involves the formation of an ylide in the presence of a base. The carbanion of this sulfur ylide is stabilized by the adjacent positively charged sulfonium ion. The reaction of the carbanion with a carbonyl group parallels that of a phosphonium ylide in the Wittig reaction. However, the decomposition of the intermediate dipolar species is different and leads to the formation of an epoxide (oxirane) rather than an alkene. 

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