Substrates, table

Alcohol dehydrogenase-catalyzed reduction of ketones is a convenient method for the production of chiral alcohols. HLAD, the most thoroughly studied enzyme, has a broad substrate specificity and accommodates a variety of substrates (Table 11). It efficiendy reduces all simple four- to nine-membered cycHc ketones and also symmetrical and racemic cis- and trans-decalindiones (167). Asymmetric reduction of aUphatic acycHc ketones (C-4—C-10) (103,104) can be efficiendy achieved by alcohol dehydrogenase isolated from Thermoanaerohium hrockii (TBADH) (168). The enzyme is remarkably stable at temperatures up to 85°C and exhibits high tolerance toward organic solvents. Alcohol dehydrogenases from horse Hver and T. hrockii... 

It is instructive to compare the amount of side products (e.g., coupling products of radicals) from the reaction of CO Me—CH2 —CH2 with a number of substrates (Table VIIIt may be sig-... 

Stockman has reported the preparation of alkyl-, aryl-, and vinyl-disubstituted aziridines with good diastereoselectivities and in good yields through treatment of tert-butylsulfmylimines with the ylide 119, derived from S-allyl tetrahydrothio-phenium bromide (Scheme 1.39) [64]. A range of substrates were tolerated, including heterocyclic, aromatic, and aliphatic substrates (Table 1.16). 

Most of these enzymes have steroids or fatty acids as their substrates (Table 1). Many P450s in endogenous biotransformation pathways are characterized by usually very narrow substrate and product specificity and by tight regulatory systems, especially those involved in steroid hormone biosynthesis. 

To overcome this drawback, we studied the arylation of diethyl 2-vinyl-[l,3]-dioxolane-4,5-diacetate 2 with several bromo polyaromatic and heteroaromatic substrates (Table 21.1 and Scheme 21.4). In parallel, the Heck coupling of several vinyl dioxolane derivatives with aryl bromides was studied in the presence of homogeneous catalysts (Table 21.1). 

Lautens and coworkers [9] ultimately used this approach to prepare a multitude of different polyheterocyclic ring systems 4-29, using 4-20 and 4-28 as substrates (Table 4.1). Unsymmetrical tethered bisfurans and acetylene dicarboxyclic acid derivatives have also been used in this domino process to allow the formation of three new rings with up to six stereogenic centers. 

A strategy to access lactones via enzymatic hydrolysis of y- and /3-hydroxy aliphatic nitriles to their corresponding acids with subsequent internal esterification was applied using commercially available enzymes from BioCatalytics Inc. A number of y- and /3-hydroxy aliphatic nitrile substrates (Table 8.11) were evaluated, with the greatest selectivity observed with y-hydroxy nonanitrile, which was converted by nitrilase NIT1003 to the precursor of the rice weevil pheromone in 30% yield, 88% ee with an enatiomeric ratio of = 23 [90],... 

Tables are organized by the functional group classes undergoing change in the substrates. Table entries are ordered by increasing carbon count of the starting substrate. Protecting groups are included in the carbon count. Unspecified yields are denoted by (—).

Each is used to some degree in nonwovens requiring flame retardancy, even though some actually impart flammability where others are inherently flame retardant. Table I summarizes the characteristics of some representative polymers widely used on rayon and polyester nonwoven substrates. Table II further identifies binder physical and chemical properties. Each binder was evaluated for its inherent flame retardancy on polyester and rayon as well as its flame retardancy in combination with commonly available flame retardants. 

Although the ruthenium allenylidene complexes 2 have not yet been as comprehensively studied as their carbene counterparts, they also seem to exhibit a closely related application profile [6]. So far, they have proven to tolerate ethers, esters, amides, sulfonamides, ketones, acetals, glycosides and free secondary hydroxyl groups in the substrates (Table 1). 

Other functional groups which have a heteroatom rather than a hydroxyl group capable of directing the hydrogenation include alkoxyl, alkoxycarbonyl, carboxylate, amide, carbamate, and sulfoxide. The alkoxy unit efficiently coordinates to cationic iridium or rhodium complexes, and high diastereoselectivity is induced in the reactions of cyclic substrates (Table 21.3, entries 11-13) [25, 28]. An acetal affords much lower selectivity than the corresponding unsaturated ketone (Table 21.3, entries 14 and 15) [25]. 

The amide group shows a prominent directivity in the hydrogenation of cyclic unsaturated amides by a cationic iridium catalyst, and much higher diastereo-selectivity is realized than in the corresponding ester substrates (Table 21.7). In the case of / ,y-unsaturated bicyclic amide (entry 3), the stereoselectivity surpasses 1000 1 [41]. An increase of the distance between the amide carbonyl and olefmic bond causes little decrease in the selectivity (d, -unsaturated amide, entry 6) compared with the case of the less-basic ester functionality (Table 21.6, entry 5). 

The parent DuPhos and BPE ligands exhibit excellent enantioselectivities routinely in excess of 95% with the majority of model a-dehydroamino acid substrates (Table 24.1) [4a, 8, 12, 13, 20, 90]. High molar SCRs (in the order of >1000 1), as well as TOFs in excess of 1000 h 1, are indicative of the high catalyst activity and productivity typically found with DuPhos and BPE systems with these simple substrates. Burk reported that in the enantiomeric hydrogenation... 

The method is applicable to a wide range of substrates. Table 4.4 gives various a, (3-enones that can be epoxidized with the La-(R)-BINOL-Ph3PO/ROOH system. The substituents (R1 and R2) can be either aryl or alkyl. Cumene hydroperoxide can be a superior oxidant for the substrates with R2 = aryl group whereas t-butyl hydroperoxide (TBHP) gives a better result for the substrates with R1 = R2 = alkyl group. 

The effects of a-CD on the bromination of other substrates have been studied recently (Javed, 1990 Tee et al., 1990a Tee and Javed, 1993), the object being to see if the catalytic effects observed earlier with phenols (Tee and Bennett, 1988a) are peculiar to these substrates or more general. Broadly speaking, various aromatic and heteroaromatic substrates (Table A4.4) showed behaviour (k /k2u = 1.7 to 10 XTS = 0.2 to 1.2 mM) very similar to that of phenols, and so the catalytic effect appears to be fairly general. The oxidation of formic acid by bromine also shows catalysis by a-CD (Han et al., 1989 Tee et al., 1990a). 

To provide an example of a reaction that is very different to electrophilic aromatic substitution, the oxidation of formic acid by bromine was also studied. This reaction, which involves electrophilic attack on the formate anion (15) (Cox and McTigue, 1964 Smith, 1972 Herbine et al., 1980 Brusa and Colussi, 1980), is catalysed by a-CD (/c /k2u = 11) (Tee et al., 1990a), and the degree of transition state stabilization (Xts = 0.18 mM) is similar to that for phenols (Table A4.2) and most of the other substrates (Table A4.4). 

Combining the results for 34 different substrates (Tables A4.2 and A4.4), there is a good correlation of logk3c with log/c2u, covering 10 orders of magnitude, with unit slope (1.01 r = 0.993) (Fig. 3). Because k3c = /c2/XB (12a), logk also correlates with logk2u in the same way. Apparently, then,... 

One more example of metal ion catalysis will be considered briefly. In a now classic paper, Cox (1974) showed that the enolization of 2-acetylpyri-dine (but not 4-acetylpyridine) is catalysed by divalent transition metal ions. Proton abstraction by acetate ions is strongly accelerated by Zn2+, Ni2+ and Cu2+ ions and the transition state stabilization by these ions roughly parallels their abilities to bind to the substrate (Table A6.5). The three metal ions are significantly superior to the proton as electrophilic catalysts, no doubt because they can chelate to both the pyridine nitrogen and the... 

The kinetic behavior of these systems is consistent with the supposition that substrate and/or catalyst molecules are freely moving around among the micelles and the bilayer vesicles much faster than the rate of reaction. However, Kunitake and Sakamoto (1978) showed that the rate of the intravesicle reaction was much faster than that of the intervesicle reaction, when p-nitrophenyl palmitate was used as substrate. Table 6 compares the rates of the intra- and intervesicle reactions in 2C12N+2C, bilayer and in CTAB micelles. A large rate difference (> 200-fold) was found in the bilayer system for the combination of cholest-Im and p-nitrophenyl palmitate. Slow transfer among vesicles of tightly bound p-nitrophenyl palmitate causes the rate difference. 

A purification scheme was devised to isolate and icjlgntify the factor for promoting photochemical reactions, by using C-mexa-carbate as the substrate (Table I). It must be noted that the factor obtained here is only partially purified. Also in some cases it requires the presence of FMN to fully express its stimulatory potency for this substrate. 

We have studied several other metal overlayers on W(110), W(100), and Ru(0001) substrates . Table 1 Usts properties of the metal overlayers, and the effect of the substrate on CO chemisorption. In general only the first monolayer grows pseudomorphically, though more than one monolayer may... 

Few examples of preparatively useful intermolecular C-H insertions of electrophilic carbene complexes have been reported. Because of the high reactivity of complexes capable of inserting into C-H bonds, the intermolecular reaction is limited to simple substrates (Table 4.9). From the results reported to date it seems that cycloalkanes and electron-rich heteroaromatics are suitable substrates for intermolecular alkylation by carbene complexes [1165]. The examples in Table 4.9 show that intermolecular C-H insertion enables highly convergent syntheses. Elaborate structures can be constructed in a single step from readily available starting materials. Enantioselective, intermolecular C-H insertions with simple cycloalkenes can be realized with up to 93% ee by use of enantiomerically pure rhodium(II) carboxylates [1093]. 

These results show that the ligand (P(et-Rf8)3) has a very low leaching in perfluorohexane. Several fluorous solvents were tested for their critical solution temperature (CST) with the substrates (Table 5). 

Schrems et al. identified a number of P,N ligands, which have given encouraging results for this class of substrate [70]. Surprisingly, the structurally simple readily accessible phosphinooxazoline 12a, originally reported by Sprinz and Helmchen [71], and subsequent analogs 12b-e proved to be the most efficient ligands for several substrates (Table 8). 

The cobalt complex is cleaved by Cl2/PPh3 with complete racemization, whereas the iron complexes may be cleaved with retention, inversion or racemization, depending on the electrophile and the substrate (Table 4). 

Secondary alkyl selenides are reduced by (TMS)3SiH, as expected in view of the affinity of silyl radicals for selenium-containing substrates (Table 4.3) [40]. Reaction (4.23) shows the phenylseleno group removal from the 2 position of nucleoside [50]. Similarly to 1,3-dithiolanes and 1,3-dithianes, five- and six-membered cyclic selenoacetals can be monoreduced to the corresponding selenides in the presence of (TMS)3SiH [51]. The silicon hydride preferentially approached from the less hindered equatorial position to give transicis ratios of 30/70 and 25/75 for the five-membered (Reaction 4.24) and six-membered cyclic selenoacetals, respectively. 

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