Sulfinates displacement

Sulfones. Sodium sulfinates displace aryl iodides in the presence of Cul in DMF. Cross-coupling of organostannanes. By catalysis of Cul, allylstannanes can react... 

Scheme 2.2 highlights Andersen s initial study, in which nucleophilic attack by ethylmagnesium iodide on enantiomerically pure (5)-(—)-menthyl p-toluene sulfinate displaces the O-menthyl leaving group to yield 62% of (R)-(-i-)-ethyl p-tolyl sulfoxide (3). 

TABLE 4. Sulfones from nucleophilic displacement of different weak leaving groups by sulfinates R1 SO2M... 

In the first mechanism (equation 74) the nucleophile function attacks the aromatic ring in an ipso-type displacement involving a Meisenheimer complex intermediate243,244, and leads to the rearranged product after expulsion of sulfinate anion (X-). This mechanism should be favoured by the presence of an electron-withdrawing substituent in conjugation with the anion. The second mechanism (equation 75) involves a direct displacement of sulfinate anion (X ) by Y-, without involvement of the aromatic n electrons. 

In reducing media, a synthetically useful variation of the Smiles rearrangement, which leads to the formation of fused ring systems, has been observed (equation 77)251. In this reaction, rearrangement is followed by displacement of the sulfinate anion by a nucleophilic o -substituent. 

Chiral allenylstannanes can be prepared by Sjv2 displacement of propargylic halides sulfinates or sulfonates with tin cuprates (Table 14)78. The nonracemic propargylic mesylate (74) afforded a nonracemic allene, [a]D —570, whose configuration was assigned by application of Brewster s rules (equation 38)78. Displacements on the steroidal mesylates 75 and 76 afforded the allenic products with complete inversion of configuration (Scheme 32)78. 

We noted earlier that the sulfinyl group of a thiolsulfinate is believed to have a basicity somewhat less than that of a sulfoxide but somewhat greater than that of a sulfinate ester (Engberts and Zuidema, 1970).+Thus, in an acid solution a thiosulfinate will be protonated to some extent to RS(OH)SR. A whole series of reactions is known that are initiated by attack of a nucleophile on the dico-ordinate sulfur of RS(OH)SR with cleavage of the S—S bond and displacement of RSOH. 

Given that the rate-determining step of the disulfide-sulfinic acid reaction is (117), and that sulfides are considerably more reactive than disulfides as nucleophiles in displacements on thiosulfonium ions (Smallcombe and Caserio,... 

A wide variety of other common nucleophiles also displaces sulfinate ion from a sulfinyl sulfone (139) very readily (Kice and Mullan, 1976). With these... 

Although not as good a leaving group as a sulfonate (ArSOj) or a halide ion (X ), a sulfinate ion (ArSOj) is still sufficiently good that it can be displaced from sulfenyl sulfur by a wide variety of nucleophiles. As a result the chemistry of thiolsulfonates is dominated by reactions of the general type shown in (167). 

The displacement of both alkoxy groups at sulfur in 239 with predominant inversion of configuration can be explained by the simultaneous formation of two different intermediates (or transition states) 242 and 243, which undergo decomposition before pseudorotation. In this context, it is interesting to note that the formation and decomposition of only one such sulfurane intermediate would give two sulfinate products with inverted and retained configuration at sulfur. 

The nucleophilic displacement of halogens by pentafluorophenoxide ion resulted in the formation of the corresponding esters [31] (equadon 29) (Table 12). Reactions of trifluaromethanesulfinyl fluoride with fluoro alcohols in the presence of sodium fluoride or cesium fluoride are used to prepare sulfinates [521 (equadon 30) (Table 12). 

The displacement of activated vinyl halides and sulfinates has also been used for the synthesis of some vinyl azides (82).24, 30,38,39... 

Chiral sulfoxides are useful intermediates in asymmetric synthesis. A number of methods for their preparation were developed in the last decade. An interesting displacement of dimethylphosphonylmethyl moiety, a carbon leaving group, from sulfur by Grignard reagents was used to obtain enantiomerically purep-tolyl sulfoxides.3 4 Optically pure methyl 4-bromophenyl sulfinate was subjected to a one-pot sequence yielding unsymmetrical dialkyl sulfoxides in 60-97% yield and >98% ee. A simple one-pot synthesis of chiral sulfoxides from norephedrine-derived... 

The seminal work of Solladid on the epimerization of sulfinate esters 50 and 51 in acidic medium in order to displace the equilibrium by precipitation of the less soluble isomer 51, permitting its isolation in 80-90% yield,84 constitutes a real breakthrough in the synthesis of sulfoxides (Scheme 14). 

Moreover, N-sulfinyl oxazolidinones have been shown to be good intermediates for the synthesis of chiral sulfinate esters and sulfinamides with excellent ee. In all cases, the absolute configuration of the sulfoxide obtained is in agreement with the fact that nucleophilic displacement occurs with inversion of configuration at the sulfur center in the starting /V-sulfinyl oxazolidinone. 

The above results may reflect on the relative stabilities of the zwitteri-onic olefin complexes, with the least alkyl-substituted olefin, viz. (XIII), affording the most stable intermediate. Displacement of the olefinic C=C from the metal by the anionic terminus of the ligand furnishes the 5-sulfinate, possibly via its 0-bonded isomer. If this substitution occurs in a concerted fashion, then the product most likely will contain a rearranged allylic fragment [Eq. (22)]. An alternative mode of collapse... 

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