A -Unsaturated sulfones

In contrast cyclic y-(rey/-butyldimethylsilyloxy)-a,/ -unsaturated sulfones undergo addition of organometallic reagents to give mainly trans-adducts after reductive removal of the sulfonyl group. 

It has long been known that a, / -unsaturated sulfones resemble a, /i-unsaturated ketones and aldehydes in undergoing addition reactions with nucleophilic reagents43. These reactions are initiated by nucleophilic attack at the carbon to the sulfone group ... 

Reaction of a-isocyano-a, / -unsaturated sulfones with primary aliphatic amines affords 1,5-disubstituted imidazoles 59 (equation 56)48. The reaction of aromatic amines such as aniline is too slow to be of practical use. Results of the preparation of 59 are listed in Table 5. 

Bromo-2-(t-butylsulfonyl)propene (79) reacts with nucleophiles such as lithium benzenethiolate, lithium enolates and Grignard reagents to give a, /(-unsaturated sulfones, which undergo nucleophilic addition of lithium cuprates (equation 68)58. 

An interesting new method for the conversion of [I, y-epoxy sulfones (82) to cyclo-alkenones (85) has been developed61. It includes the addition of alkyllithium to y-hydroxy-a,/ -unsaturated sulfones generated from 82 and the alkylation of sulfonyl carbanion thus formed. Oxidation of the resulting y-hydroxy sulfone to 84 followed by elimination of benzenesulfinic acid gives the desired product 85 in good yields (equation 72)61. 

TABLE 9. Preparation of cyclopropanes 111 from a,/ -unsaturated sulfones 109 and a-metallated nitriles 11071... 

Arenesulfonyl chlorides77 as well as alkenesulfonyl chlorides78 react with vinylarenes in the presence of RuCl2(PPh3)3 and 1 molar equiv. of Et3N to form a,/ -unsaturated sulfones in 70-90% yields. The reaction mechanism for the ruthenium(II) catalyzed reaction involves a free-radical redox-transfer chain process as outlined below77 ... 

Allylic sulfones and a, -unsaturated sulfones are known to be in equilibrium ... 

Allylic sulfones, such as 242, isomerize to a, -unsaturated sulfones 243 upon treatment with a catalytic amount of potassium t-butoxide in dry THF. The a, -unsaturated sulfones can be converted to the corresponding olefins upon desulfonation with sodium amalgam or aluminium amalgamSince treatment of allylic sulfones with potassium-graphite gives 2-alkenes, alkylation of allylic sulfones and subsequent desulfonation is a useful process for the synthesis of olefins, as shown in Scheme 6. 

Nucleophilic addition to a, -unsaturated sulfones has long been known. For example, treatment of divinyl sulfone with sodium hydroxide has been known to afford bis( -hydroxyethyl) sulfone "", while the reaction of a- and -naphthyl allyl sulfones and allyl benzyl sulfone " with alkali hydroxide or alkoxide gave -hydroxy or alkoxy derivatives. In the latter reaction, the allyl group underwent prototropy to the 1-propenyl group, which in a subsequent step underwent nucleophilic attack . Amines, alcohols and sulfides are known to add readily to a, -unsaturated sulfones, and these addition reactions have been studied widely. In this section, the addition of carbon nucleophiles to a, ji-unsaturated sulfones and the reactions of the resulting a-sulfonyl carbanions will be examined. 

This chapter deals with (1) the transformation of the sulfone functionality into other functional groups by nucleophilic substitution reaction, and (2) the addition and elimination reaction of a, -unsaturated sulfones. Particular attention will be paid to recent uses of sulfones in organic syntheses. ... 

The central bond of the l-(arylsulfonyl)bicyclo[1.1.0]butane system behaves like the double bond of a, ) -unsaturated sulfones to give alkyl-substituted cyclobutyl aryl sulfones on treatment with organometallic reagents (equation 20). This method has been applied... 

IV. ADDITION REACTIONS OF a, UNSATURATED SULFONES A. Addition of Nucleophiles to a, Unsaturated Sulfones... 

Nucleophiles such as alkyllithium, or the anion derived from 2-nitropropane, readily add to y-hydroxy-a, ) -unsaturated sulfones (equations 69 and 70) . Oxidation followed by elimination of t-butylsulfmic acid leads to the formation of dienones (equation 70). 

Deprotonation of the vinylic proton is a serious side-reaction in the conjugate addition of organometallic reagents to y-siloxy-a, -unsaturated sulfones (89) . The use of the... 

Since the first demonstration of a cycloaddition reaction of a, -unsaturated sulfones in 1938 by Alder and coworkers , a variety of a, jS-unsaturated sulfones have been prepared and used as dienophUes. For example, when a mixture of p-tolyl vinyl sulfone and 2,3-dimethylbutadiene in benzene is heated at 145-150°C for 10 h in a sealed tube, crystals of the cycloadduct (134) are obtained (equation 102). Other examples of this intermolecular cycloaddition reaction are given in Table 12. 

The sulfonyl group in sulfones resists catalytic hydrogenation. Double bonds in a, -unsaturated sulfones are reduced by hydrogenation over palladium on charcoal (yield 94%) [686, 687] or over Raney nickel (yield 62%) without the sulfonyl group being affected [686]. In p-thiopyrone-1,1-dioxide both double bonds were reduced with zinc in acetic acid but the keto group and the sulfonyl group survived [655]. Raney nickel may desulfurize sulfones to hydrocarbons [673]. 

The CM of vinyl sulfones is of great synthetic value, as a,/ -unsaturated sulfones are becoming increasingly utilized in stereocontrolled organic synthesis.The compatibility of remote sulfone and sulfoxide moieties in RCM and is well established. However, initial attempts to employ catalyst 3 in the CM of methyl vinyl sulfones... 

Marino has reported that the fluoride-induced ring cleavage of l-silyloxy-2-carboalkoxycyclopropanes affords -y-oxo-a-ester enolates, modified homoenolates, which add to Michael acceptors to afford cyclopentanes and cyclopentenes, e.g. (258—>259) 196 alternatively, a carboannulation procedure affords octalin-l-ones (260—>261 Scheme 87) (note the intramolecular enolate addition to the a, -unsaturated sulfone). 

This reaction can also be induced thermally (10, 315). The adducts are useful precursors to a,/ -unsaturated sulfones, obtained on oxidation with H202 or... 

Silylcuprates have been reported to undergo reactions with a number of miscellaneous Michael acceptors [65]. Conjugate addition to 3-carhomethoxy acyl pyri-dinium salts [65a] affords 4-silyl-lj4-dihydropyridines. Oxidation with p-chloranil generates a 4-acyl pyridinium salt that gives the 4-silylnicotinate upon quenching with wateq and methyl 4-silyl-2-suhstituted dihydronicotinates upon quenching with nudeophiles (nudeophilic addition at the 6-position). The stabilized anion formed by conjugate addition to an a, -unsaturated sulfone could he trapped intramolecularly by an alkyl chloride [65h]. 

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