Phosphorus and Sulfur Nucleophiles

Click Coached Tutorial Problems for more practice in drawing the products of the Alkylation of Actetylide Anions. 

Suggest methods for preparing these compounds from alkyl halides  

Sulfur occurs directly beneath oxygen in the periodic table. Therefore, sulfur compounds are weaker bases but better nucleophiles than the corresponding oxygen compounds. Sulfur compounds are excellent nucleophiles in SN2 reactions, and because they are relatively weak bases, elimination reactions are not usually a problem. Yields are good with primary and secondary substrates. For similar reasons, phosphorus compounds also give good yields when treated with primary and secondary substrates in Sn2 reactions. The following equations provide examples of the use of these nucleophiles  

CHAPTER 10 SYNTHETIC USES of substitution and elimination reactions 

Triphenylphosphine is probably the most important phosphorus nucleophile for organic chemists because it produces phosphonium salts (see the preceding two equations). These phosphonium salts are starting materials for an important preparation of alkenes that will be discussed in Chapter 18. 

---

In order to achieve maximum specific radioactivity, in target production of [ C]methane followed by iodination is the method of choice. Alkylation reactions on oxygen, nitrogen, phosphorus, and sulfur nucleophiles as well as on carbanions indeed cover a large variety of... 

The chlorine atom in l-(a-chloroalkyl)benzotriazole is readily replaced by a wide range of carbon, nitrogen, phosphorus, oxygen, and sulfur nucleophiles, for example, 1-chloromethylbenzotriazole... 

The lack of reactivity of 3-halo substituents under non-radical nucleophilic substitution conditions allows differential functionalization of pyri-dines by 3-umpolung and 2-nucIeophilic substitution processes. Thus, treatment of 2-fluoro-3-iodopyridine (189) with oxygen or amine nucleophiles affords products 191 which, upon subjection of SRN1 reactions with carbon, phosphorus, and sulfur systems, give 2,3-difunctionalized pyri-dines 192 (Scheme 56) (88JOC2740). 

A nucleophile adds, forming a trigonal bipyramidal pentacovaient intermediate that then ejects the leaving group in the microscopic reverse of the nucleophilic addition reaction. The pentacovaient intermediate is often short-lived, and this is shown by enclosing it in brackets. The pentacovaient intermediate bonds that are colinear are called axial (or apical) bonds, whereas the three bonds that lie in the plane perpendicular are called equatorial. Three common elements that can react by this pathway are silicon, phosphorus, and sulfur. Hydrolysis of phosphate esters like RNA occurs by this path. 

Miller, B., Reactions of 4-bromocyclohexadienones with nucleophiles containing phosphorus and sulfur, J. Org. Chem., 28, 345, 1963. 

Extensive studies on the molybednum complex XXXVI with various bidentate phosphorus and sulfur, ligands demonstrate that hydride, n-butyllithium and cyanide nucleophiles add to the arene to give XXXVII ... 

Clearly, the chemistry of LR is a fascinating blend of phosphorus and sulfur chemistry. Its success hinges as much on the nucleophilicity of sulfur as on the oxophilicity of pentavalent phosphorus. 

Nucleophilic Substitution at the Nitrogen, Phosphorus, and Sulfur Centers... 

Nucleophilic Substitution at the Nitrogen, Phosphorus, and Sulfur Centers performed synthesis of the salts of the tricoordinate sulfuranide anion [170,171] ... 

Nagelkerke, R., Thatcher, G.R.J., Buncel, E. Alkali-metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. IX. p-Nitrophenyl diphenyl phosphate. Org. Biomol. Chem. 2003,1, 163-167. 

Recently developed trifluoromethylatmg agents capable of transferring the trifluoromethyl group as a cation to strongly nucleophilic compounds such as carbanions and sulfur and phosphorus nucleophiles are prepared from o-biphenyl trifluoromethyl sulfoxide [164] and are shown in equation 141... 

In addition there are certain other methods for the preparation such compounds. Upon heating of the thionocarbonate 2 with a trivalent phosphorus compound e.g. trimethyl phosphite, a -elimination reaction takes place to yield the olefin 3. A nucleophilic addition of the phosphorus to sulfur leads to the zwitterionic species 6, which is likely to react to the phosphorus ylide 7 via cyclization and subsequent desulfurization. An alternative pathway for the formation of 7 via a 2-carbena-l,3-dioxolane 8 has been formulated. From the ylide 7 the olefin 3 is formed stereospecifically by a concerted 1,3-dipolar cycloreversion (see 1,3-dipolar cycloaddition), together with the unstable phosphorus compound 9, which decomposes into carbon dioxide and R3P. The latter is finally obtained as R3PS ... 

We shall discuss first reactions in which hydrogen or a metallic ion (or in one case phosphorus or sulfur) adds to the hetero atom, and then reactions in which carbon adds to the hetero atom. Within each group, the reactions are classified by the nature of the nucleophile. Additions to isocyanides, which are different in character, are treated at the end. 

---