Formation of adducts

Anhydro bases can attack the a-position, e.g. of thiazolium cations, with the formation of adducts capable of oxidation to cyanine dyes, e.g. Scheme 18 (see Section 4.02.3.3.4). 

The formation of adducts of enamines with acidic carbon compounds has been achieved with acetylenes (518) and hydrogen cyanide (509,519,520) (used as the acetone cyanohydrin). In these reactions an initial imonium salt formation can be assumed. The addition of malonic ester to an enamine furnishes the condensation product, also obtained from the parent ketone (350,521). 

The reaction of dialkylaminobutenynes with 1,2- and 1,3-dimercaptoalkanes also involves the formation of adducts of 1,3-orientation (85USSRP1109401 88ZOR88), but with retention of the initial butenyne dialkylamino group, in contrast to the reaction with 1,2-diaminoethane. Thus, with 1,2-dimercaptoethane, 1-dialkylaminobut- l-en-3-ynes form 7-dialkylamino-5-methyl-7//-2,3-dihydro-1,4-dithiepins (105) in 90-96% yield (85USSRP1109401 88ZOR88). 

Wlien tlie diiral molybdenum -K-allyl-substituted enone 147 was treated witli litliium dimetliylciiptate, formation of adduct 148 witli fait selectivity was observed tSdieme 6.29) [69], Interestingly, bigber selectivities were obtained in tlie presetice of boron ttlbuotlde etlierate. It is assumed tliat Lewis acid coordination induces tlie s-trans reactive conformation 149 [64], Consequently, nudeopb de attack anti to tlie molybdetiLim ftagmetit sbould afford tlie major diastereomer 148. 

Previously studied possibilities for bromine storage systems are listed in Table 1. The widely known reduction of the Br2 vapor pressure by formation of adducts with various carbon materials results from strong chemisorption interactions and has Table 1. General possibilities for bromine storage... 

Crystalline, diastereomerieally pure syn-aIdols are also available from chiral A-acylsultams. lhe outcome of the induction can be controlled by appropriate choice of the counterion in the cnolate boron enolates lead, almost exclusively, to one adduct 27 (d.r. >97 3, major adduct/ sum of all other diastereomers) whereas mediation of the addition by lithium or tin leads to the predominant formation of adducts 28. Unfortunately, the latter reaction is plagued by lower induced stereoselectivity (d.r. 66 34 to 88 12, defined as above). In both cases, however, diastereomerieally pure adducts are available by recrystallizing the crude adducts. Esters can be liberated by treatment of the adducts with lithium hydroxide/hydrogen peroxide, whereby the chiral auxiliary reagent can be recovered106. 

The formation of adduct is followed by fragmentation and subsequent H-atom abstraction reaction from the sulfinic acid produced. Strong acid solutions of aromatic sulfoxides like thianthrene 5-oxide (7) or phenothiazine 5-oxide (8) gives rise to ESR signals, which... 

The formation of adducts may confuse the assignment of molecular weight. 

Chromyl chloride oxidation of alkenes proceeds via the formation of adducts at a rate necessitating stopped-flow techniques. At 15 °C the formation of 1 1 adduct from styrene and oxidant in CCI4 solution is simple second-order with 2 = 37.0 l.mole .sec . Measurements with substituted styrenes yielded = — 1.99. E = 9.0 kcal.mole and = —23.8eu for styrene itself. Hydrolysis of the styrene adduct yields mostly phenylacetaldehyde (76.5 %)and benzaldehyde (21.1 %). Essentially similar results were obtained with a set of 15 alkenes and... 

This scheme shows that cyanide sourced from smoking or otherwise (see 6.3.7) may determine the metabolism of chrysotherapeutic agents. [Au(CN)2] anions bind to serum albumin predominantly by the formation of adducts without the displacement of cyanide [94]. The ions bind tightly to albumin independent of the oxidative state of Cys-34. The equilibrium constant values for [Au(CN)2] binding to serum albumin are similar to values for other gold complexes that bind to albumin. This indicates that albumin can act as a carrier for transporting [Au(CN)2] in the bloodstream. 

If cellular redox state, determined by the glutathione status of the heart, plays a role in the modulation of ion transporter activity in cardiac tissue, it is important to identify possible mechanisms by which these effects are mediated. Protein S-,thiolation is a process that was originally used to describe the formation of adducts of proteins with low molecular thiols such as glutathione (Miller etal., 1990). In view of the significant alterations of cardiac glutathione status (GSH and GSSG) and ion-transporter activity during oxidant stress, the process of S-thiolation may be responsible for modifications of protein structure and function. 

In a like way P2O3CI4 reacts with metal chlorides 65,86), where at least with the Lewis acids among them, a primary formation of adducts, e.g. SbClj P2O3CI4, is likely 87,65) ... 

A detailed description of sources used in atmospheric pressure ionization by electrospray or chemical ionization has been compiled.2 Atmospheric pressure has been used in a wide array of applications with electron impact, chemical ionization, pressure spray ionization (ionization when the electrode is below the threshold for corona discharge), electrospray ionization, and sonic spray ionization.3 Interferences potentially include overlap of ions of about the same mass-charge ratio, mobile-phase components, formation of adducts such as alkali metal ions, and suppression of ionization by substances more easily ionized than the analyte.4 A number of applications of mass spectroscopy are given in subsequent chapters. However, this section will serve as a brief synopsis, focusing on key techniques. 

Formation of Adducts with Main-Group Acids... 

These results suggest that the transition states leading to the formation of the cyclo-adducts (33) and (34) are product-like and that the greater than statistical formation of adducts (34) is due to the increased thermodynamic stability of a trisubstituted double bond. In agreement with this explanation is the fact that in reactions with for example p-xylene and durene (1,2,4,5-tetramethylbenzene) only the adducts (35) and (36) were obtained 54-59). Also as expected, two adducts were obtained with tetralin but only the compound (37) was obtained using 5,8-dimethyltetralin, which we may regard as a 1,2,3,4-tetra-alkylben-zene 54>. 

When reactions with oxygen-containing acceptors were performed [3] in the 300-400°C region, the formation of adducts occurred with both Tetralin and mesitylene. This reaction was observed when benzyl radicals were generated from dibenzyl ether, dibenzyl sulfide, benzyl alcohol, and benzaldehyde. 

The most surprising observation from low temperature reactions was the formation of adducts between good donor solvents (Tetralin, octahydrophenanthrene, tetrahydroquinoline) and acceptor radicals. The resulting adducts were not of a single predominant structure. In particular, several isomers of toluene-Tetralin were formed as well as di-Tetralin. Several of these reactions were done with D -Tetralin which permitted the firm identification of the Tetralin moiety in the adducts. GLC-MS studies indicated that the Tetralin may be bonded to phenyl, benzyl, benzyloxy- or phenoxy-groups, depending on the acceptor used. 

Modern MCRs that involve isocyanides as starting materials are by far the most versatile reactions in terms of available scaffolds and numbers of accessible compounds. The oldest among these, the three-component Passerini MCR (P-3CR), involves the reaction between an aldehyde 9-1, an acid 9-2, and an isocyanide 9-3 to yield a-acyloxycarboxamides 9-6 in one step [8], The reaction mechanism has long been a point of debate, but a present-day generally accepted rational assumption for the observed products and byproducts is presented in Scheme 9.1. The reaction starts with the formation of adduct 9-4 by interaction of the carbonyl compound 9-1 and the acid 9-2. This is immediately followed by an addition of the oxygen of the carboxylic acid moiety to the carbon of the isocyanide 9-3 and addition of this carbon to the aldehyde group, as depicted in TS 9-5 to give 9-5. The final product 9-6 is... 

Photoproducts arising by a [3 + 2] cycloaddition of s-triazolo[4,3-b]-pyridazine (269) to alkenes have been described.222 Addition to cyclohexene, for example, led to the formation of adducts 270 and 271, and the proposed mechanism is outlined in Scheme 8. The reaction has been extended to include addition to cis- and rans-hex-3-ene,223 cyclooctene,224 and furan.225... 

Psoralens can react by two different routes upon photoactivation (Parsons, 1980 Pathak, 1984). The first route is through the well-known photoreaction mechanism that principally involves intercalation within double-stranded DNA or RNA with the formation of adducts with adjacent thymine bases. The furan-side and pyrone-side rings in psoralen both can form cycloaddition products with the 5,6-double bond of thymine to create a crosslink between two DNA strands (Reaction 57) or to a lesser extent, within double-strand regions of RNA. 

Due to rapid proton exchange between forms 22, 23, and 24 (Scheme 1), benzotriazole exhibits at room temperature just two C-H signals, each for two protons, in its 111 NMR spectra. However, when the temperature is lowered, the signals broaden and finally split into four separate resonances of the four individual C-H protons. The results of such study for an acetone solution of benzotriazole are given in Table 3 <2002T9089>. The situation is additionally complicated by formation of adducts 25 and 26, which at — 90 °C contribute 25% and 5%, respectively, to the total molecular population. 

Electrocyclic closure of butadiene units encased within cycloheptane rings has been used to obtain bicyclo[3.2.0]heptene systems (Scheme 5)12. For example, irradiation of eucarvone 21 led to the formation of adduct 22 in 52% yield via a disrotatory ring closure123. This adduct was used as a key intermediate in the synthesis of the pheromone grandisol, 23, which proceeded in 20% overall yield from 22. In their synthesis of a-lumicolchicine. Chapman and coworkers utilized a photochemically initiated four-electron disrotatory photocyclization of colchicine to produce /Murnicolchicine 24a and its /-isomer 24b in a 2 1 ratio12b. These adducts were then converted, in a second photochemical step, to the anti head-to-head dimer a-lumicolchicine 25. 

Despite the enormous importance of dienes as monomers in the polymer field, the use of radical addition reactions to dienes for synthetic purposes has been rather limited. This is in contrast to the significant advances radical based synthetic methodology has witnessed in recent years. The major problems with the synthetic use of radical addition reactions to polyenes are a consequence of the nature of radical processes in general. Most synthetically useful radical reactions are chain reactions. In its most simple form, the radical chain consists of only two chain-carrying steps as shown in Scheme 1 for the addition of reagent R—X to a substituted polyene. In the first of these steps, addition of radical R. (1) to the polyene results in the formation of adduct polyenyl radical 2, in which the unpaired spin density is delocalized over several centers. In the second step, reaction of 2 with reagent R—X leads to the regeneration of radical 1 and the formation of addition products 3a and 3b. Radical 2 can also react with a second molecule of diene which leads to the formation of polyene telomers. 

Allyl radicals can, of course, also be generated by electrolysis of the corresponding /J,y-unsaturated carboxylic acids together with a second carboxylic acid. This mixed Kolbe electrolysis method has been used to study the recombination of allyl radical 32 with the undecyl radical 3370. Recombination leads to the formation of adducts 34 and 35 in a ratio of 72 28, again preferring the product with the higher substituted double bond (equation 16). 

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