Reaction with multiple bonds

In view of the stereochemical behavior in the additions to alkenes and dienes, the authors suggest that the reaction proceeds via a stepwise electrophilic addition126. However, in this case the two sulfur atoms of the dithioether dication are positively charged. In the reaction with multiple bonds, therefore, one of these sulfur atoms should be an electrophilic center whereas the other one should simultaneously be a nucleophilic center. In... 

The reactivity of heteroatom-substituted stannenes has not been fully reported so far. On the other hand, those of tetraarylstannenes 26 and 27 and transient stannenes 33 and 34 have been widely investigated (Scheme 2.9.10). These compounds readily undergo 1,2-addition with various protic reagents and iodomethane. Their reactions with multiple-bond compounds such as ketones, butadienes, and azides result in the formation of the corresponding [2- -n]-cycloadducts (n = 2, 3,4). 

Schrock carbene complexes undergo reaction with multiple bonds via four-center metallacyclic intermediates (51). Chapter 11 will consider what occurs when alkylidenes react with alkenes, a reaction known as alkene metathesis. Below are examples of Schrock carbenes reacting with polar multiple bonds such as C-N and C=0. 

Megati S, Phadtaie S, Zemlicka J (1992) Unsaturated phosphonates as acyclic nucleotide analogs. Anomalous Michaelis-Arbuzov and Michaelis-Becker reactions with multiple bond systems. J Org Chem 57 2320-2327... 

Most of these reactions were carried out in sealed tubes. Gel2 also reacts with multiple bonds 127). 

In contrast to the high regioselectivity and good yields of electroreductive intramolecular coupling reactions of ketones with multiple bonds shown in Schemes 34 to 37, the yields of interm olecular coupling reactions have been very low until recently. However, by using carbon fiber electrodes, intermolecular coupling reactions have... 

While the concerted pathway has been preferred in early publications on the subject, evidence for a stepwise mechanism involving distonic ion intermediates is presented in more recent work taking kinetic isotope effects into account. [90] This is also in agreement with the postulation that reactions involving multiple bonds are generally stepwise processes. [37,91] Nevertheless, this question is still a matter of debate. [90]... 

Compounds with multiple bonds, e.g. alkenes, alkynes, aromatics, can also act as nucleophiles in so-called electrophilic reactions (see Chapter 8). 

Addition and substitution reactions of heteroatom-centered radicals with multiple bonds have been extensively studied and are sometimes preparatively useful.11 This section will briefly consider the addition reactions of H—Y and X—Y reagents (Kharasch reactions) and substitution reactions (Scheme S6).245... 

When a reaction involves multiple bonding changes, a question may arise whether the bonding changes occur by a stepwise or concerted pathway. An answer to such a question based on the classical reaction theory is that the reaction proceeds by a concerted pathway, by a stepwise pathway, or by a mixture of the two separate pathways. However, if one takes into account dynamic effects, the answer to the question of concerted versus stepwise may be much more complex. It is interesting to point out here that the case reported by Singleton for the ene reaction affords a case, where stepwise mechanism can dynamically operate on a concerted PES. This contrasts with the reactions described in section Nonstatistical Product Distribution , in which the... 

The following reactions proceed with the participation of the allylic boron system (i) allylboration and protolytic cleavage of organic compounds with multiple bonds, (ii) allylboron-alkyne condensation,598 599 (iii) reductive mono-and trans-a,a -diallylation of nitrogen aromatic compounds, (iv) disproportionation processes between tribut-2-enylborane and BX3 (X = C1, Br, OR, SR). Allylboration of carbonyl compounds, thioketones, imines, or nitriles leads to the homoallylic alcohols, thiols, or amines (Equations (136) and (137). It is most important that 1,2-addition to aldehydes and imines proceeds with high diastereoselectivity so that ( )-allylic boranes and boronates give the anti-products, while -products are formed preferentially from (Z)-isomers. 

Addition of hydrogen to compounds with multiple bonds, such as the formation of ethane from ethylene or acetylene. Rideal1 found 137° C. to be the optimum temperature for the hydrogenation of ethylene, and considers the mechanism of the process to be explicable on the hypothesis of Langmuir 2 that the reaction proceeds in a unimolecular film on the surface of the nickel catalyst. 

In addition to substrates of type X—Y where on reaction the X—Y bond is broken, compounds with multiple bonds may add oxidatively without X—Y bond cleavage, to give new complexes that have three- membered rings. In effect, one component of the multiple bond is broken and employed... 

In spite of the progress in investigating the mechanism of the reaction of ozone with multiple bonds, another pathway of the reaction mentioned in [16], in which ozone is the donor of atomic oxygen, has not been studied yet. 

A major distinction for nucleophilic reactions with ambident anions is whether they proceed with kinetic or thermodynamic control.80 N-Substituted saccharins (10) should be thermodynamically more stable because of amide character than the isomeric pseudosaccharin (3) of imidate structure. In fact 3 may be rearranged thermally to 10 in an irreversible reaction.96 The threshold for thermodynamic control appears to be lowered for electrophiles with multiple bonds, e.g., formaldehyde, reactive derivatives of carboxylic acids, but also quaternary salts of N-heterocyclic compounds.80 It will be seen that in those cases substitution indeed occurs at the nitrogen, not necessarily through thermodynamic control. 

Germylenes have long been known to react with multiple bonds such as C=C, C C, and C=0. In addition, insertion reactions into carbon halogen, O H, and N H bonds, are well precedented. In the last 10 years, substantial progress has been made in the reaction with C H bonds. 

In Chapters 10 and 11 we turn our attention to alkenes and alkynes, compounds that contain one and two n bonds, respectively. Because n bonds are easily broken, alkenes and alkynes undergo addition, the third general type of organic reaction. These multiple bonds also make carbon atoms electron rich, so alkenes and alkynes react with a wide variety of electrophilic reagents in addition reactions. 

Desvergne, J.-P., Bouas-Laurent, H. (1990), Cycloaddition Reactions Involving 4n Electrons [2 + 2] Cycloadditions Molecules with Multiple Bonds Incorporated in or Linked to Aromatic Systems, in Photochromism, Molecules and Systems Durr, H., Bouas-Laurent, H., Eds. Elsevier Amsterdam. 

There are a number of different classes of catalyst modifiers acids and bases, metal cations, nucleophilic species, and compounds with multiple bonds which are strongly chemisorbed. >54.55 a general description of each of these classes is given below. More detailed descriptions of the use of particular modifiers in specific reactions will be found in Section III. 

---