Heteroatom Multiple Bonds

Cycloadditions of benzonitril-4-nitrobenzylide to a variety of carbon to heteroatom multiple bonds including methyl dithiobenzoate and dimethyl trithiocarbonate (Scheme 148), X = MeS or Ph, have been examined in detail by Huisgen et al. (757). 

In contrast to the related organoboranes, which are mostly used in the addition to non-polar carbon-carbon multiple bonds, aluminum hydrides have found their widest use in organic synthesis in the addition reaction to polar carbon-carbon and carbon-heteroatom multiple bonds including carbonyl, nitrile and imino groups as well as their a,(J-unsaturated analogs. Although these reduction reactions are also sometimes referred as hydroalumination reactions in the Hterature, they are outside the scope of this review. 

In addition to undergoing cycloaddition reactions with alkenes and al-kynes, silenes readily undergo cycloaddition reactions with heteroatom multiple bonds such as C=0 and C=N, most commonly when the trapping reagent for the silene is either an aldehyde, ketone, or imine. In many... 

The N=N double bond of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) (177) is undoubtedly the most studied heteroatom-heteroatom multiple bond involved in reactions with MCPs. 

In the scope of this subsection, competitive 1,3-cycloaddition of nitrile oxides to carbon-carbon and carbon-heteroatom multiple bonds are of special interest. Competition between carbon-carbon and carbon-nitrogen double bonds in... 

Kumada s use of a ferrocene moved away from the C2-symmetrical motive, as planar chirality can result from the two ferrocene rings having different substituents. The development of this class of ligand is well documented [5, 125-127]. The best-known uses of these ligands are for reductions of carbon-heteroatom multiple bonds, as in the synthesis of the herbicide, Metolachlor [128, 129]. 

Addition of radicals to carbon-carbon or carbon-heteroatom multiple bonds followed by the trapping of resulting radicals with a hydrogen atom source... 

Carbon-heteroatom multiple bonds can also participate in cycloaddition reactions with carbonyl ylides leading to the synthesis of interesting heterocycles (Scheme 4.18). 

In addition to olefins, carbon heteroatom multiple bonds can also participate in the cycloaddition with various carbonyl ylides (Scheme 4.28). 

Due the nature of the substituents, all the stable singlet carbenes exihibit some carbon-heteroatom multiple-bond character and for some time their carbene nature has been a subject of controversy. One has to keep in mind that apart from dialkyl-carbenes, all the transient singlet carbenes present similar electronic interactions. As early as 1956, Skell and Garner drew the transient dibromocarbene in its ylide form based on the overlap of the vacant p-orbital of carbon with the filled p orbitals of the bromine atoms (Scheme 8.31). 

General an Index The general a -index (GAI) applies to molecules that contain heteroatoms, multiple bonds, and cis/rrans-specified double-bond locations [30], This approach is based on the orbital interaction graph of linked atoms (OIGLA) and the orbital interaction matrix of linked atoms (OIMLA). The GAI is computed as the absolute value of the determinant of OIMLA ... 

Addition reactions to other carbon-heteroatom MULTIPLE BONDS (see also Grignard reaction, Hydrolysis, Reduction reactions)... 

Addition reactions of carbon radicals to C—O and C—N multiple bonds are much less-favored than additions to C—C bonds because of the higher ir-bond strengths of the carbon-heteroatom multiple bonds. This reduction in exothermicity (additions to carbonyls can even be endothermic) often reduces the rate below the useful level for bimolecular additions. Thus, acetonitrile and acetone are useful solvents because they are not subject to rapid radical additions. However, entropically favored cyclizations to C—N and C—O bonds are very useful, as are fragmentations (see Chapter 4.2, this volume). 

The following introduction will briefly recount some of the key features of radical cyclizations with an emphasis on basic concepts that control regio- and stereo-selectivity. More details will be provided in the following sections, which describe specific types of reactions. The factors affecting the cyclization reactions to carbon-heteroatom multiple bonds are treated separately in Section 4.2.5, and the cyclizations of heteroatom-centered radicals are contained in Section 4.2.4. 

Recent advances in the chemistry of silicon-heteroatom multiple bonds... 

Recent advances in the chemistry of silicon-heteroatom multiple bonds 1065 B. Theoretical Calculations 1. Silanones and silanethiones... 

---