Substituted by Heteroatoms

The polarized C-X bonds in aliphatic organic halides are electrophilic and can be attacked readily by various nucleophilies. These reactions 

2-octyl, P-O2NC6H4-, p-AcCeH4-, 2-benzothiazolyl X = Cl, Br, I, tosylate, MeSOa-) in the presence of Bu4NBr and 30% aqueous KOH 

R s R Y/phase-transfer catalyst benzene/aqNaOH, r.t. 15min R R 

In basic aqueous media, a kinetic study of the reaction between stannate(II) ions and alkyl halide shows that mono- and disubstituted organotin compounds are formed (Eq. 6.12a). The monosubstituted organotin compound is obtained after a nucleophihc substitution catalyzed by a complexation between the tin(II) and the halide atom. The disubstituted compound results from an electrophihc substitution coupled with a redox reaction on a complex between the monosubstituted organotin compound and the stannate(II) ion. Stannate(IV) ions prevent the synthesis of the disubstituted compound by complexation. Similarly, when allyl bromide and tin were stirred in D2O at 60° C, allyltin(II) bromide was formed first. This was followed by further reaction with another molecule of allyl bromide to give diallyltin(IV) dibromide (Eq. 6.12b).  

Synthesis of 2-alkyl- or 2-aryl-substituted benzo[b]furans has been reported, involving a CuI-TMEDA complex which catalyzes the transformation of readily available ketone derivatives into the corresponding benzofurans in good-to-excellent yields in water (Eq. 6.13).  

---

Several examples for allylic reagents further substituted by heteroatoms are known. For example, a mixture of the l,l-dichloro-2-alkene and the l,3-dichloro-1-alkene leads to a homogeneous homoallylic alcohol17,18. 

This review concerns in the first part the works published during the last three years on the synthesis and reactivity of stabilized ylides C-substituted by electron-withdrawing groups (COR, CO2R, CN, etc.). The second part deals with the works published in the same period on the chemistry of phosphorus ylides mainly C-substituted by heteroatoms of groups 1-16 (metals, metalloids and nonmetal elements Li, Ba, Ca, Ti, Zr, Nb, Mo, Re, Fe, Ru, Rh, Pd, Pt, Au, Zn, Hg, B, Si, Sn, N, P, As, Sb, O, S, Te). 

The second chapter (M. Taillefer and H. J. Cristau) is dedicated to new trends in ylide chemistry. The preparation and the reactivity of phosphorus ylides, C-substituted by heteroatoms is presented, ylides being substituted by groups 1 and 2 elements, by transition metals or by elements of groups 13 to 16. A rich and versatile chemistry is thus reported. 

Scheme 19 Cyclic 7i-conjugated systems fully substituted by heteroatoms... 

Experimentally, it has been shown that the introduction of a heteroatom such as oxygen into the 4-position of piperidine has no appreciable influence on the conformational equilibrium348. Similarly, infrared overtone measurements suggest that in tetrahydro-1,2 oxazine the NH-equatorial conformer predominates349. On the other hand, many piperidines substituted by heteroatoms in the 3 position are found to exhibit a NR axial preference. For example, the preferred conformation for the molecules shown below is NR axial350,35... 

Heteroatom-containing derivatives of pentalene and azulene are 8- and 10-jr-electron systems, respectively, and have been extensively studied by Hafner and co-workers.301-304 A few examples are presented in Schemes 30, 47, and 86. Electron-rich azapentalenes 247—249305 306 and various aza-azu-lenes 250—252300-302 have intense colors and are stable but oxygen-sensitive compounds. Azulenes with nitrogen heteroatoms placed in positions with high electron density, such as position 5, or positions 5 and 7, present a hypsochromic effect, while a heteroatom in position 6, with low electron density, exerts a bathochromic effect. When both types of positions are substituted by heteroatoms, their effect is canceled out.307 The bond lengths in 252 (Scheme 86), as determined by X-ray, indicate delocalization as in 252a and 252b.308 309... 

Potassium hydroxide, 258 Trimethylsilyl chlorochromate, 327 of carbon-carbon double bonds substituted by heteroatoms m-Chloroperbenzoic acid, 76 of oximes to carbonyl compounds Lithium aluminum hydride-Hexa-methylphosphoric triamide, 159 Titanium(III) chloride-Diisobutylalu-minum hydride, 303 Trimethylsilyl chlorochromate, 327 of protected alcohols Chlorodimethylthexylsilane, 74 Formic acid, 137 p-Methoxyphenol, 181 of thioacetals and -ketals Methoxy(phenylthio)trimethyl-silylmethane, 182... 

Several porphyrin analogues with the pyrrolic nitrogens substituted by heteroatoms have been synthesized, but only the oxa analogues (23 X = O, Y = NH) are reported to form stable metal complexes (Figure 8). 60 Formation of a Zn complex of the thia analogue (23 X = S, Y = NH) requires the presence of a large excess of Zn" ion. An iron complex of dithiaporphyrin (23 X = Y = S) is also known. 

The importance of carbanions a-substituted by heteroatoms in organic synthesis explains the vast amount of literature concerning the use of a-heterosubstituted organotins in transmetallation reactions. As the tin-lithium exchange is assumed to occur with a complete retention of configuration at the carbanion centre639, the enantioselective approach of such stabilized carbanions for synthesis has been the subject of recent developments. 

The dioxetanyl ring carbons, if not substituted by heteroatoms, are located characteristically at 5 (TMS) 88-90 ppm. ITeteroatom substitution shifts this resonance in expected amounts to lower fields. The specific values are listed for the individual derivatives in Table 1. 

Substitution Patterns Covers 12 different substitution patterns that typically occur. These patterns are based on replacing atom groups with chlorine atoms to treat them as similar. Four criteria can be defined for atom groups to be replaced atoms directly attached to aromatic rings, atoms attached to carbon-carbon multiple bonds, bond orders to substituents, and multiple substitutions by heteroatoms. 

Thermodynamical Properties of Ethylenes Substituted by Heteroatoms or Functional Groups (in kcal mol"1)... 

Biellmann JF, Ducep JB (1982) Allylic and benzylic earbanions substituted by heteroatoms. Org Reactions 27 1, John Wiley... 

Wood, M.G. Suhadolnik, J.G. Ravichandran, R. Lau, J. Hendricks-Guy, C. Bulliard, C. Benzotriazoles containing alpha-cumyl groups substituted by heteroatoms and compositions stabilized therewith, U.S. Patent 6,451,887, September 17, 2002. 

---