Allylic sulfonylations

Similarly, enamino vinyl sulfones (345) can undergo a thermally allowed electrocyclic reaction between the termini of the enaminic double bond and the allyl sulfonyl portion in the intermediate anion (346) to afford a, /1-unsaturated thiene dioxides (348) as shown in equation 126335. 

The allylic sulfonyl group is regioselectively cleaved in the presence of the alkyl-sulfonyl group by indirect reduction with anthracene as a mediator (Fig. 24) [125]. 

The allylic sulfonyl allene 35, possessing unsymmetrical substitution at the distal double bond of the allene, was examined. Since there are two possible sites for y5-hy-dride eliminahon, a variety of isomers are possible. Treatment of allene 35 with [Rh(CO)2Cl]2 gave a 3 5 1 raho of the three possible products 36, 37, and 38, which translates into an 8 1 constitutional group selectivity in the y5-hydride elimination step ((364-37) 38) and an T/Z-selechvity of 1 2 (Tab. 8.8, entry 1). 

Other nucleophiles have been used in this reaction. For example, BINAP was shown to be the best ligand for the enantioselective allylic amination of 19 with sodium diformylamide, a protected ammonia equivalent, furnishing the desired product in good yield and excellent enantioselectivity [96]. Also, a P,N-ligand has been developed for the allylic sulfonylation with good ee but moderate yield [97]. 

After conversion to unsaturated sulfonates through reaction with vinyl or allyl sulfonyl chlorides, both primary and secondary alkenols afford dihydro-1,2-oxathiane 2,2-dioxides through a Ru-catalysed RCM (Scheme 55) <06T9017>. 

Chuard et al. used allylsulfoxides as precursors of oxygen-centered radicals (Scheme 83) [229]. The Evans-Mislow rearrangement of allylsulfoxides leads to allyl sulfonyl ethers. The authors decided to use those as source of oxygen radicals. In addition, when the allyl sulfoxide was branched on a cyclobutene, the tandem reaction delivered a cyclobutyloxy radical that collapsed and underwent ring expansion in good overall yield. Thus, starting from sulfoxide 283,... 

Allylic sulfonyl carbanions react with electrophiles such as alkyl halides and aldehydes at the a-position. Although relatively strong bases like Bu"Li and LDA are usually used for deprotonation of allylic sulfur compounds, including sulfones, a catalytic two-phase system that consists of a concentrated aqueous NaOH solution and a quaternary ammonium salt can be used to generate allylic sulfonyl carbanions. 1,1-Dilithiated allyl phenyl sulfone (equation 20) reacts with excess benzaldehyde to afford the 1,3-( )-diadduct, while l,ort/io-dilithiated allyl phenyl sulfone gives the l,ort/io-diadduct predominantly. Other examples of sulfur-substituted allylic anions are summarized in Table 1. 

Li and coworkers have reported BiuNI-catalyzed allylic sulfonylation of a-methyl styrene derivatives with sulfonyl hydrazides 143 using TBHP (Bu OOH) as the terminal oxidant (Scheme 4.73) [115]. The mechanism of this reaction involves the generation of sulfonyl radicals, Ts, from sulfonyl hydrazides 143 by the BU4NI/TBHP catalytic system, followed by the addition of Ts to a-methyl styrene derivatives 142 to give the corresponding allylic sulfones 144. 

Allylic sulfonylations can also be accomplished by using the iron nitrosyl complex 31 as catalysts [98]. In these cases, 2-methoxylethanol was used as a co-solvent to DMF due to the poor solubility of the sodium sulfinate substrate to be applied as a nucleophile. The effect of the phosphine ligand was also investigated. Tuning efforts revealed an outstanding performance of P(p-MeOAr)3 as co-catalyst. These efforts rendered a suitable protocol for efficient and regioselective allylic sulfonylation allowing C-S bond formations, as depicted in Scheme 37. 

P-stereogenic diazaphospholidines are good ligands for Pd-catalysed allylic sulfonylation, in which sodium /jara-toluenesulfinate acts as a -nucleophile furnishing allylic sulfones (Scheme 8.12 and Table 8.5). 

From Table 8.5 is clear that the diazaphospholidine moiety is an excellent chiral inductor for allylic sulfonylation, although the yield is sometimes unsatisfying (entries 1, 3 and 5). The ligand of entry 1 is remarkable because of its extremely high enantioselectivity given its very simple structure. 

Table 8.5 Selected examples of Pd-catalysed allylic sulfonylation of 11 (Scheme 8.12).

Davidson and coworkers introduced a new CarroU-variant in which tertiary allylic ) -sulfonyl esters underwent [3,3]-sigmatropic rearrangements to y,d-unsaturated sulfones [30]. As seen in Scheme 8.35, ambruticin, an antifungal agent, was envi-... 

As the previous shown amination reaction, Lyubimov et al. [54b,58] investigated the palladium-catalyzed allylic alkylation with dimethyl malonate and allylic sulfonylation of ( )-l,3-diphenylallyl... 

SCHEME 22.13 Asymmetric allylic alkylation and allylic sulfonylation of (Sl-l.S-diphenylallyl acetate. 

Allylic sulfonylation with sodiumpara-toluenesulfinate was investigated with ligands 46 and 47, where the catalytically active species was prepared in situ (Table 22.23). The same effect as in the previous allylic substitution reaction was observed. The electron-withdrawing ligand 47 led to a decrease in conversion and enantiomeric excess, whereas with the electron-donating ligand 46 full conversion and an ee of up to 92% were observed. 

Palladium-Catalyzed Allylic Sulfonylation of (f)-1,3-diphenylallyl Acetate with Sodium para-Toluenes... 

By analogy with the catalytic allylic alkylation performed with C-nucleo-philes described in Section 7.2.2.3, Plietker et al. used benzyl mercaptan as an S-nucleophile toward an isobutyl carbonate in the presence of an NHC-Fe complex 9. Allylic thioethers were obtained in 82% yield as a mixture of two regioisomers [eqn (7.7)]. The same group also investigated the sulfonylation of allylic carbonates with a-sulfonyl succinimides as S-nucleop-hiles. In this case, a base-free catalytic system generated in situ by thermal release of the SIMes carbene from its chloroform adduct in the presence of [Bu4N][Fe(CO)3(NO)] was adopted. Addition of DBU to the reaction mixtures allowed the one-pot synthesis of vinyl sulfones through a tandem iron-catalysed allylic sulfonylation/amine-catalysed isomerisation process. Remarkably, base-induced decomposition of the iron catalyst was not observed. 

Eichelmann H, Gais H. Palladium-catalyzed asymmetric allylic sulfonylation. Tetrahedron Asymm. 1995 6 643-646. 

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