Addition reaction described

Other Related Reactions In addition to simple 1,4-addition reactions described so far, other related rhodium-catalyzed asymmetric carbon-carbon bond-forming processes have also been developed. Lautens reported an asymmetric ring-opening of... 

The yields obtained after 10 min in a batch reactor with MgO, CaO, or SrO exceeded 92%, whereas with BaO the yield was lower (72%), probably because of its low surface area (2m /g). When alkaline earth hydroxides were used as basic catalysts, the yields were lower than for the corresponding oxides. The most active hydroxides were Sr(OH)2 8H2O and Ba(OH)2 8H2O, which gave the additional compound in yields of 75% and 70%, respectively, whereas carbonates were characterized by very poor activity. As observed for other reactions, the catalytic activity of MgO strongly depends on the pre-treatment temperature. A maximum in activity was observed when MgO was pre-treated at 673 K. At this temperature, decomposition of Mg(OH)2 to MgO is not complete, and Mg(OH)2 remains in the catalyst. It was suggested that the surface OH groups act as active sites, as for the Michael addition reactions described above. 

There are many addition reactions of a,(3-unsaturated aldehydes, ketones, and related compounds that are the same as the carbonyl addition reactions described previously. Others are quite different and result in addition to the alkene double bond. Organometallic compounds are examples of nucleophilic reagents that can add to either the alkene or the carbonyl bonds of conjugated ketones (see Section 14-12D). Hydrogen cyanide behaves likewise and adds to the carbon-carbon double bond of 3-butene-2-one, but to the carbonyl group of 2-butenal ... 

Additional reactions described in the scheme above include ... 

Table 5 lists several reactions in which the Grignard reagent is added to a system that allows ring-opening or displacement, rather than the typical addition reactions described previously. Umezawa [42] patented an approach to make long-chain alcohols from optically active epoxides (see Table 5, entry 1). In this example, they prepared optically pure 4-decyl alcohol in quantitative yield. The product was formed by the addition of a Grignard reagent to the epoxide a catalyst, copper(I) iodide, was also used. 

A two-center version of the oxidative addition reaction described above has also been observed by Wayland with porphyrinato Rh-Rh-bonded dimers [23]. By using a sterically encumbered ligand, such as tetramesitylporphyrin (TMP), the Rh-Rh bond energy is considerably reduced, permitting the formation of a (TMP)Rh-R and a (TMP)Rh-H species (Scheme 1). 

Relatively little is known concerning the reactions of radicals with alkaline earth oxides however, Smith and Tench [Ref.23] reported that H- reacts with MgO to form Fs centers (electrons trapped at anion vacancies) and OH" ions. This is similar to the reductive addition reaction described above, and by analogy one Scheme I... 

As in alkenes, the pi electrons of alkynes are exposed to electrophilic attack (see Figure 3.17). Therefore, many addition reactions described for alkenes also occur, though usually more slowly, with alkynes. For example, bromine adds as follows ... 

The acyl addition reactions described in this chapter will occur with carboxylic acid derivatives, but rarely with carboxylic acids. Remember that... 

From the analysis of NH3 conversion and product yields we speculate that NH3 oxidation was inhibited by NO2, specifically in the low-T region (T < 275 °C), resulting in a decrease of the NH3 conversion with increasing NO2 feed contents. Despite experimental evidences, a detailed mechanistic study of this phenomenon was not in the scope of this study. On the other hand, in addition to the inhibited NH3 oxidation reactions, the NOx consumption observed in the low-T range justified the introduction of two additional reactions describing the reactivity between NH3 and NO2 with simultaneous formation of N2O and of N2 (R.22 in Table 18.2) or of N2 only (R.23 in Table 18.2). Second-order kinetics in ammonia surface coverage and NO2 gas phase concentration were adopted for both reactions (R.22) and (R.23). 

Transamination reactions are occasionally used as an adjunct to the addition reactions described in this section. Aniline and /3-di-ethylaminopropionitrile (as hydrochloride) undergo amine exchange at 140-150° to give )8-anilinopropionitrile (reaction 83) 1 . These... 

The addition reactions described so far are carried out in the absence of molecular oxygen, as a general approach for radical chain reactions. Alkanethiyl radi-... 

According to this reaction scheme, HO2 radicals are formed similar to the processes of H-atom abstraction forming alkanes seen in Sect. 7.2.2. Since OH radicals are regenerated from HO2, HOx chain reactimi cycle is completed, and NO is oxidized to NO2 simultaneously. However, the ratio of H-atom abstraction is only a few percent in the case of toluene, and it has been know from the product analysis that the main pathway is addition reaction described below (Klotz et al. 1998 Calvert et al. 2002 Atkinson and Arey 2003) (Reaction Scheme 7.9). 

Alkenes are commonly described as unsaturated hydrocarbons because they have the capacity to react with substances which add to them Alkanes on the other hand are said to be saturated hydrocarbons and are incapable of undergoing addition reactions... 

With certain other nucleophiles addition takes place at the carbon-carbon double bond rather than at the carbonyl group Such reactions proceed via enol intermediates and are described as conjugate addition ox 1 4 addition reactions... 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

An analogous preparation of thioxopenams from dithiocarbonates (75, R = t-C4H2(CH2)2Si, R = OC H ) has also been described (115). Additionally, an iatramolecular Michael addition reaction to form the [2,3] bond has been exploited ia penem synthesis to prepare FCE 22101 (69) (116). 

Reversible inhibition is characterized by an equiUbrium between enzyme and inhibitor. Many reversible inhibitors are substrate analogues, and bear a close relationship to the normal substrate. When the inhibitor and the substrate compete for the same site on the enzyme, the inhibition is called competitive inhibition. In addition to the reaction described in equation 1, the competing reaction described in equation 3 proceeds when a competitive inhibitor I is added to the reaction solution. 

In addition to the reactions described in the preceding section, alkyl groups in the 2-positions of imidazole, oxazole and thiazole rings show reactions which result from the easy loss of a proton from the carbon atom of the alkyl group which is adjacent to the ring (see Section 4.02.3.1.2). 

Ochrymowycz and his coworkers have also prepared a number of polysulfur macrocycles for use in biological or biological model systems . The synthetic methodology is essentially similar to that described above except that certain of the sulfur containing fragments were prepared by addition reactions to ethylene. Two examples of this approach, taken from ref. 59, are shown in Eq. (6.9). 

In addition to the reactions described under the Preparation, the anhedrides undergo the following changes. ... 

The purpose of the present review is to indicate the methods that have been used to obtain quantitative equilibrium and kinetic data for this water-addition reaction and to discuss the results that have so far been reported. It is hoped that by describing some of the characteristics of this reaction recognition of further examples may be facilitated. 

An interesting addition reaction of sulfur dichloride has been discovered that allows the preparation in good yield of bridged cyclic sulfides from cyclic dienes. Two examples of the reaction have been described (cyclo-octadiene and in the other 1,5-cyclooctadiene. The former sequence is shown in the scheme. The experimental details of the latter sequence are given below. 

Conjugated dienes also undergo electrophilic addition reactions readily, but mixtures of products are invariably obtained. Addition of HBr to 1,3-butadiene, for instance, yields a mixture of two products (not counting cis-trans isomers). 3-Bromo-l-butene is the typical Markovnikov product of 1,2-addition to a double bond, but l-bromo-2-butene appears unusual. The double bond in this product has moved to a position between carbons 2 and 3, and HBr has added to carbons 1 and 4, a result described as 1,4-addition. 

Additional evidence of the reaction described in Equation (11) is the section of the Li2C03 -Nb02F system s melting diagram presented in Fig. 9 [87]. 

With a-alkyl-substituted chiral carbonyl compounds bearing an alkoxy group in the -position, the diastereoselectivity of nucleophilic addition reactions is influenced not only by steric factors, which can be described by the models of Cram and Felkin (see Section 1.3.1.1.), but also by a possible coordination of the nucleophile counterion with the /J-oxygen atom. Thus, coordination of the metal cation with the carbonyl oxygen and the /J-alkoxy substituent leads to a chelated transition state 1 which implies attack of the nucleophile from the least hindered side, opposite to the pseudoequatorial substituent R1. Therefore, the anb-diastereomer 2 should be formed in excess. With respect to the stereogenic center in the a-position, the predominant formation of the anft-diastereomer means that anti-Cram selectivity has occurred. 

The first reports on enantioselective addition reactions of achiral organometallic reagents, modified by aprotic chiral additives, described the addition of Grignard reagents to prostereogenic carbonyl compounds in the presence of ( + )-(/ ,/J)-2,3-dimethoxybutane (l)4 5, (-)-tetrahydro-2-methylfuran (2)6, (-)-l-[(tetrahydro-2-furanyl)methyl]pyrrolidine (3)7 or (-)-sparteine (4)8. The enantioselectivity, however, was poor (0-22% ee). 

Synthon Reagent Section D. Describing Carbonyl Addition Reactions With ... 

---