Phenylsulfonyl groups

Lithiated indoles can be alkylated with primary or allylic halides and they react with aldehydes and ketones by addition to give hydroxyalkyl derivatives. Table 10.1 gives some examples of such reactions. Entry 13 is an example of a reaction with ethylene oxide which introduces a 2-(2-hydroxyethyl) substituent. Entries 14 and 15 illustrate cases of addition to aromatic ketones in which dehydration occurs during the course of the reaction. It is likely that this process occurs through intramolecular transfer of the phenylsulfonyl group. 

Phenylsulfonylfulminic acid, prepared as outlined in Scheme 110, reacted even with highly hindered alkenes such as tetramethylethylene. The phenylsulfonyl group was easily displaced by a variety of nucleophiles such as methoxide, cyanide and hydride (79JA1319). 

CF3CO2H, Me2S, 40-60 min, 100% yield, [Imidazole = His(Tos)]." The related phenylsulfonyl group has been used to protect pyrroles and indoles, and is cleaved with NaOH/H20/dioxane, it, 2 h. " ... 

Addition of the anion occurs anti to the bulky acctonide moiety of the 1,3-benzodioxole while alkylation of the intermediate sulfonyl anion occurs from the axial direction which ensures that the phenylsulfonyl group remains equatorial. 

Kaplan and Martin s116 determinations for phenylsulfinyl and phenylsulfonyl groups are of interest as showing practically no difference in or values, with a very small negative oR for SOPh, cf. Taft s values for SOMe and S02Me. 

Trost and coworkers7 have reported the use of palladium(O) as a catalyst for displacement of the phenylsulfonyl group by soft nucleophiles. Thus, treatment of allyl sulfone 12 with the sodium salt of dimethyl malonate in the presence of 5 mol % of... 

Remarkable solvent effects on the selective bond cleavage are observed in the reductive elimination of cis-stilbene episulfone by complex metal hydrides. When diethyl ether or [bis(2-methoxyethyl)]ether is used as the solvent, dibenzyl sulfone is formed along with cis-stilbene. However, no dibenzyl sulfone is produced when cis-stilbene episulfone is treated with lithium aluminum hydride in tetrahydrofuran at room temperature (equation 42). Elimination of phenylsulfonyl group by tri-n-butyltin hydride proceeds by a radical chain mechanism (equations 43 and 44). 

The phenylsulfonyl group attached at the 3-position of isoxazolines (132) is readily substituted by a variety of nucleophiles (equation 101), as summarized in Table ll84. 

Acylation with imidazolides of a cyclopropane-CH activated by a phenylsulfonyl group proceeded under ring-enlargement to give a dihydrofuran system [103a]... 

Nitroalkenes with potential leaving groups in (3-position such as a dialkylamino, an alkylthio, or a phenylsulfonyl group undergo addition-elimination reactions with nucleophiles. The chemistry of nitroenamines has been extensively investigated, and their potential utility in organic synthesis has been well established.2613 116 Severin and coworkers have developed the addition of elimination reactions of nitroenamines with carbon nucleophiles in 1960-1970, as exemplified in Eq. 4.94.117... 

This procedure illustrates a highly selective and facile method for introducing a phenylsulfonyl group into the Z-position of 1,3-diene systems by using commercially available starting materials. The method can be applied to cyclic as well as acyclic systems giving 2-(pheny1sulfonyl)-l,3-dienes. In an alternative synthesis via condensation of allyl sulfone with aldehyde and subsequent acylation-elimination, the 2-(phenylsulfonyl)-l,3-dienes obtained are limited to acyclic systems. 

This approach involves additions of alkyl radicals to C=N bonds and snbseqnent fi-expulsion of the phenylsulfonyl group (as a radical) which react with bis(trialkyl)tin to propagate a chain. The phenylsulfonyl group lowers the energy of the LUMO of the radical acceptor, increasing the rate of addition of alkyl radicals . 

Nitrothiophene reacts with a sulfone to afford 2-phenyl-4-phenylsulfonylthieno[2,3- ]pyridine, 91, in low yield <1998T2607>. The phenylsulfonyl group can be readily replaced by a variety of nucleophiles. 

A -Sulfonyl-2,2 -biindoles undergo a formal [4-I-2] cycloaddition with various dienophiles to produce indolocarba-zoles <2004TL4009>. Thus, reaction of 171 with A -benzylmaleimide in chlorobenzene in a sealed tube produces the cycloadduct in moderate yield (Equation 105) as the only observable product (Table 11). It is proposed that the reaction proceeds by an initial Michael addition, followed by a rapid cyclization and loss of the phenylsulfonyl group during the aromatization process. Similar cyclization reactions are observed with A -methylmaleimide, dimethylace-tylene dicarboxylate, and 1,4-naphthoquinone. 

Of particular interest are cases in which substituents are present in ortho positions to the reacting methyl group. Apart from o-chloro-substituted derivatives, those with methoxy, carbonamido, sulfonamido, and phenylsulfonyl groups have been reported to undergo reaction.68 The 2-(3-chloro-4 methyIphenyl)-5-methoxybenzotriazole (163) has been found to be particularly reactive, yielding, with Schiff s base 98, the stilbene 164.54... 

Among the many variants that add two heteroatoms, those that add phenylsulfonyl groups are particularly useful because they proceed in high yield under mild conditions and provide functionality for subsequent synthetic transformations. The examples contained in Scheme 88 illustrate some recent applications.230-232 In contrast to most radical additions to alkynes, the additions of ArS X are often highly stereoselective. 

The use of isopropylidine acetals (112) as tethers in the intramolecular Diels-Alder reactions of dienes with alkenes facilitates the formation of civ-fused cycloadducts (113) from an endo transition state (Scheme 41).218 The intramolecular Diels-Alder reaction of 4-[tris-(2-mcthylcthyl)silyl]oxy-2//-thiopyran derivatives with potential dienophiles tethered at C(2), C(3), C(5), and C(6) positions yielded cycloadducts when the dienophiles were activated with a carbomethoxy group.219 By the substitution of a phenylsulfonyl group on the dienophile of 2-benzopyran-3-ones, it is possible to enhance exo addition during intramolecular Diels-Alder cyclizations to yield a predominance of trans-fused hexaphenanthrenes related to natural products.220 The intramolecular Diels-Alder reaction of 2-furfuryl fumarates has been investigated by molecular mechanics (SIBFA)/continuum reaction field computations.221 The intramolecular 4 + 2-photo-cycloaddition of A-benzylcinnamamides (114) in the presence of C(,H6 gives 3-azatricyclo[5.2.2.01,5]undeca-8,10-dien-4-ones (115) with high stereoselectivity (Scheme 42).222... 

Simple alkyl(phenyl)iodonium salts are not stable. However, when there is in a-position the bulky, electron-withdrawing phenylsulfonyl group they are stabilized, like their precursors, i.e. ArS02CH2I(00CCF3)2. Iodanes of this type were coupled with benzene in presence of CF3S020Tf to afford isolable ArS02CH2I+Ph TfO [142]. 

The nucleophilic addition of lithiated allyl phenyl sulfone to nitrones has proceeded exclusively a to the phenylsulfonyl group affording anti adducts in high yield.47 At (g 0 °C isoxazolidines have been obtained with complete al -trans selectivity. 

Reaction with -alkylthio nitro olefins. Nitro alkenes bearing an alkylthio or phenylsulfonyl group at the -position undergo addition-elimination reactions with organocopper/zinc reagents to provide functionalized (E)-nitro alkenes. 

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