Allylic anions sulfur-substituted

If the donor is a sulfur atom, its lone pair is practically nonbonding (the electronegativities of sulfur and carbon are similar), above 2 and scheme c is no longer valid. If the sulfur is modeled by a carbanion, the sulfur-substituted diene and the dienophile are represented by the pentadienyl and the allyl anions, respectively. Their HOMOs will both be nonbonding. Hence FO theory predicts that placing the sulfur on the dienophile and the attractor on the diene may be slightly more favorable than the opposite substitution pattern. 

Cyclizations. A route to substituted naphthalenes by intramolecular cyclization involves attack by a nascent allyl anion to a ketone group. On the other hand, the generation of N-arylindolines from arylamines and o-halostyrenes is a more complex process. Arylamines. The Pd-catalyzed arylation of amines depends critically on l-BuOK. Synthesis of sulfur compounds. a-Sulfenylation under mild conditions is realized... 

X-substituted AUyl Anions. The allyl-lithium reagents 4.53-4.56 are relatively simple examples of X-substituted allyl anions. With oxygen303,304 or nitrogen305,306 substituents, 4.53 and 4.54, y alkylation is almost always the major pathway, but with sulfur, while y alkylation is known307 4.55, a alkylation is much more common 4.56.308,309... 

Table 1 Reaction of Sulfur-substituted Allylic Anions with Electrophiles...

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. 

Reaction of certain sulfur-substituted allylic anions with Ti(0-i-Pr)4 produces a 3-(alkylthio)allyltitanium reagent that condenses, through its a-terminus, with aldehydes to give onri-p-hydroxy sulfides in a highly stereo- and regioselective manner (eq 18). These latter compounds can be transformed, stereoselectively, into froar-vinyloxiranes or 1,3-dienes. ... 

A new class of nucleophiles have been introduced for sulfur addition. Degl Innocenti and his group [145, 146] have shown that allyl or benzylsi-lanes, in the presence of tetra-n-butylammonium fluoride, reacted in a thiophilic fashion and led to allyl sulfides or dithioacetals. It is remarkable that this selective reaction is general for a large variety of thiocarbonyl compounds thioketones [145], dithioesters [146], and even with the normally sluggish trithiocarbonates [145]. With substituted allyl silanes retention of configuration of the allyl chain is observed. It is noteworthy that the possible [2,3] sigmatropic shift of the intermediate anionic species was not observed. 

Surprisingly, this anion is also a good soft nucleophile and attacks saturated carbon atoms through the sulfur atom. In this case attack occurs at the less substituted end of an allylic bromide to give an allylic sulfone, which we will use later on. 

Asymmetric Coiyugate Addition of Allyl- and Crotylphosphonamides/ The asymmetric C-allylation of a, 3-unsaturated carbonyl compounds is a powerful tool for the functionalization of a carbonyl compound in the P-position. Since such a process normally leads to the corresponding enolate derivative when anionic reagents are used, there exists the possibility of trapping with an electrophile. Thus sequential addition and trapping can lead to vicinally substituted carbonyl compounds. Asymmetric allylation has been achieved previously with simple cycloalkenones using phosphorus and sulfur based reagents that must be prepared in diastereomerically pure form. 

Propargylic Anion Equivalent. (TMS)allene reacts with electrophiles at the C-3 position in an Se2 process analogous to electrophilic substitution reactions of allyl- andpropargylsilanes. For example, upon treatment with trimethylsilyl chlorosulfonate or sulfur trioxide-1,4-dioxane, (TMS)allene yields silyl esters of sulfonic acids (eq 3). (TMS)allene undergoes conjugate addition with a, 8-unsaturated acyl cyanides to yield 5,e-acetylenic acyl cyanides. ... 

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