Reactivity pattern scheme

The solvent-stabilized cations [Cp2ZrR(solvent)]+ shows typical reactivity patterns (Scheme 12). Hydrogenolysis of the... 

In 2013, the first successful generation of ds-homoenolate equivalents from ds-enals under the catalysis of N-heterocyclic carbene D4 was developed by the Chi group. The ds-homoenolate intermediates I undergo effective reaction with a,p-unsaturated imines to afford chiral cyclic ketones 62. Compared to the trans-enals, ds-enals show different stereoselectivities and new reactivity patterns (Scheme 20.29). 

The second communication of that year [24] is now cited more than 225 times, which also represents a remarkable number. This communication also comprised new reactivity patterns (Scheme 2). Based on the results from the first communication discussed above, a furan ring is formed from an allenyl ketone. Then the furanyne intermediate underwent a previously unknown transformation to an annelated phenol. Since they are easily accessible, furanynes can also be used directly. 

The preparation and spectroscopic properties (infrared, ultraviolet, NMR) of iV-alkoxycarbonyl-N -(2-thiazolyl)thioureas (268) have been studied by the Nagano group (78, 264). These compounds react with bromine in acetic acid or chloroform to give 2--alkoxycarbonylimino-thiazolo[3,2-h]thiadiazolines (Scheme 162), whose structures were established by mass spectroscopy, infrared, NMR, and reactivity patterns (481). 

In the revised Patterns scheme reactivity ratios involving S are used as reference reactions.15415 Reactivity ratios are then given by eqs. 60 and 61 ... 

The Patterns scheme has been tested for its capacity to predict nC NMR chemical shifts of the CH7- carbon of monomers (CH =CXY)159 and in evaluating the reactivities of small radicals towards monomers.160... 

Reaction scheme, defined, 9 Reactions back, 26 branching, 189 chain, 181-182, 187-189 competition, 105. 106 concurrent, 58-64 consecutive, 70, 130 diffusion-controlled, 199-202 elementary, 2, 4, 5, 12, 55 exchange, kinetics of, 55-58, 176 induced, 102 opposing, 49-55 oscillating, 190-192 parallel, 58-64, 129 product-catalyzed, 36-37 reversible, 46-55 termination, 182 trapping, 2, 102, 126 Reactivity, 112 Reactivity pattern, 106 Reactivity-selectivity principle, 238 Relaxation kinetics, 52, 257 -260 Relaxation time, 257 Reorganization energy, 241 Reversible reactions, 46-55 concentration-jump technique for, 52-55... 

As mentioned earlier, metal complexation not only allows isolation of the QM derivatives but can also dramatically modify their reactivity patterns.29o-QMs are important intermediates in numerous synthetic and biological processes, in which the exocyclic carbon exhibits an electrophilic character.30-33 In contrast, a metal-stabilized o-QM can react as a base or nucleophile (Scheme 3.16).29 For instance, protonation of the Ir-T 4-QM complex 24 by one equivalent of HBF4 gave the initial oxo-dienyl complex 25, while in the presence of an excess of acid the dicationic complex 26 was obtained. Reaction of 24 with I2 led to the formation of new oxo-dienyl complex 27, instead of the expected oxidation of the complex and elimination of the free o-QM. Such reactivity of the exocyclic methylene group can be compared with the reactivity of electron-rich enol acetates or enol silyl ethers, which undergo electrophilic iodination.34... 

The coordinated quinone methide Jt-system of complex 24 can also undergo cycloaddition (Scheme 3.17). When 24 was reacted with /V-methylmaleimide, a [3+2] cycloaddition took place to give the tricyclic iridium complex 29. The closest example to this unprecedented reactivity pattern is a formal [3 + 2] cycloaddition of /)-quinone methides with alkenes catalyzed by Lewis acids, although in that reaction the QMs serve as electron-poor reagents. 36... 

Diazomalonic esters, in their behavior towards enol ethers, fit neither into the general reactivity pattern of 2-diazo-l,3-dicarbonyl compounds nor into that of alkyl diazoacetates. With the enol ethers in Scheme 17, no dihydrofurans are obtained as was the case with 2-diazo-l,3-dicarbonyl compounds. Rather, copper-induced cyclo-propanation yielding 70 occurs with ethoxymethylene cyclohexane u4). However,... 

Although the existence and structures of tetraorganozincates in the solid state are now well established, the reactivity patterns of these compounds in organic synthesis are still largely unknown. Homoleptic and heteroleptic tetrasubstituted dianionic zincates of the type [ZnR3X], X = Me, CN, SCN, were prepared as shown in Scheme 58... 

An interesting finding was made by changing of the connectivity (1,1 instead of 1,2) of the central olefin moiety of the substrate, that is, the usual diene product 324 from the skeletal rearrangement was observed in this case (Scheme 83). The fact that by using rhodium instead of platinum or ruthenium, the reactivity pattern is totally different also suggests all the subtlety and complexity of the mechanism of these transformations.302... 

Zirconocene-catalyzed kinetic resolution of dihydrofurans is also possible, as illustrated in Scheme 6.8 [18]. Unlike their six-membered ring counterparts, both of the heterocycle enantiomers react readily, albeit through distinctly different reaction pathways, to afford — with high diastereomeric and enantiomeric purities — constitutional isomers that are readily separable (the first example of parallel kinetic resolution involving an organome-tallic agent). A plausible reason for the difference in the reactivity pattern of pyrans and furans is that, in the latter class of compounds, both olefmic carbons are adjacent to a C—O bond C—Zr bond formation can take place at either end of the C—C 7T-system. The furan substrate and the (ebthi)Zr-alkene complex (R)-3 interact such that unfavorable... 

Scheme 6.13. Zr-catalyzed enantioselective alkylation with neat Et3AI can lead to an alternative reactivity pattern (formation of 39 rather than 40).

However transient and elusive cationic zirconocenes may be, they are real and some of their salts have been isolated and characterized, both spectroscopically and by X-ray crystallography. None of these cations is ever completely free they are either coordinated by an additional ligand (typically a solvent molecule) or they interact with their counterions, no matter how non-coordinating these may be [16], Scheme 8.1 shows the typical reactivity pattern of a solvent-stabilized cation [Cp 2ZrR(solvent)]+ (A Cp = q5-C5H4Me)... 

The general idea of this concept was first outlined by Nugent and Rajan-Babu [17-20] as shown in Scheme 3, and constitutes an analogue of the well-established opening of a cyclopropylcarbinyl radical [21,22]. Titanocenes have emerged as the most powerful reagents in these transformations. However, it is clearly attractive to find other metal complexes in order to develop novel reactivity patterns. 

Aryl- and alkylsulfonyl radicals have been generated from the corresponding iodides and added to, e.g., propadiene (la), enantiomerically enriched (P)-(+)-propa-2,3-diene [(P)-(lc)] and (P)-(-)-cyclonona-l,2-diene [(P)-(lk)] [47]. Diaddition of sulfo-nyl radicals may compete considerably with the monoaddition [48,49]. Also, products of diiodination have been purified from likewise obtained reaction mixtures, which points to a more complex reactivity pattern of these substrates towards cumulated Jt-bonds. An analysis of regioselectivities of arylsulfonyl radical addition to allenes is in agreement with the familiar trend that a-addition occurs in propadiene (la), whereas alkyl-substitution at the cumulated Jt-bond is associated with a marked increase in formation of /3-addition products (Scheme 11.7). 

R-Me andAn-Me alloys. A summary of the alloying behaviour of the 3rd group metals with special attention to the compound formation capability is shown in Fig. 5.14. For the lanthanides two examples are shown La and Gd, the behaviour of which may be considered to give a reasonable first approximation description of the general intermetallic reactivity pattern of the lanthanides. For the actinides the reactivity schemes are shown for Th, U and Pu for the alloys of the other metals of this series, only a few data are available. 

As far as the use of ferrocene molecules as potentiometric sensors is concerned, they are part of the more general reactivity pattern illustrated in Scheme 12. 

Of great interest are the "donor-acceptor-substituted cyclopropanes" 19, such as 2-silyloxycyclopropanecarboxylic esters (19a), first reported by Reissig [19b] and then also studied independently by Marino [20]. The general reactivity pattern of cyclopropanes 19 is outlined in Scheme 5.15 [19a]. 

The unique reactivity pattern of alkynyl iodonium salts discussed in Sections II,A.2 and II,D,la can also serve as two-carbon conjunctive reagents in the synthesis of pyrroles, dihydropyrroles, and indoles. Feldman et al. found that combination of alkyl or aralkyl tosylamide anions 101 with phenyl(propynyl)iodonium triflate (102) furnishes the corresponding dihydropyrroles 103 (95JOC7722) (Scheme 28). 

Laser flash photolysis of 46 showed results similar to those obtained for 45. The lifetimes and yields of Z and E photoenols from 46 are comparable to those obtained for 56. Similarly, laser flash photolysis of 47 reveals that the major reactivity pattern of 47 is intramolecular H-atom abstraction to form Z-58 and E-58 even though no products were observed that can be attributed to the formation of photoenol 58. Laser flash photolysis of 47 in methanol showed formation of biradical 57 ( max 330 nm, r = 22ns), which was efficiently quenched with oxygen (Scheme 32). Biradical 57 intersystem crosses to form Z-58 and E-58, which have maximum absorption at 400 nm. Enols Z-58 to E-58 were formed in the approximate ratio of 1 4. Enol Z-58 had a lifetime of 6.5)0,s in methanol, but its lifetime in dichloro-methane was only 110 ns. The measured lifetime of E-58 in methanol was 162)0,s, while it was 44 ms in 2-propanol. Thus, E-58 is considerably shorter-lived than E-56. Furthermore, E-58 is also shorter-lived than the analogous E-59 (Scheme 33), which cannot decay by intramolecular lactonization and has a lifetime of 3.6 ms in methanol. Thus, we proposed that E-58 undergoes solvent-assisted reketonization that is facilitated by the intramolecular H-atom bonding, as shown in Scheme 34. 

The chemistry outlined in Schemes 8.32 and 8.34 illustrates the complexity of reactions that occur between thiocarbonyl compounds and diazo compounds. Heimgartner and co-workers (214-217) observed a similar reactivity pattern when they combined l,3-thiazol-5(477)-thiones (153) with diazoalkanes. When ethyl diazoacetate was used, additional reaction pathways occurred giving rise to a complex mixture of products (218). An interesting aspect of this chemistry involves... 

The above model has been further explored to account for reaction efficiencies in terms of a scheme where nucleophilicities and leaving group abilities can be rationalized by a structure-reactivity pattern. Pellerite and Brau-man (1980, 1983) have proposed that the central energy barrier for an exothermic reaction (see Fig. 3) can be analysed in terms of a thermodynamic driving force, due to the exothermicity of the reaction, and an intrinsic energy barrier. The separation between these two components has been carried out by extending to SN2 reactions the theory developed by Marcus for electron transfer reactions in solutions (Marcus, 1964). While the validity of the Marcus theory to atom and group transfer is open to criticism, the basic assumption of the proposed model is that the intrinsic barrier of reaction (38)... 

SCHEME 72. General reactivity pattern of zinc-copper reagents... 

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