Bond stereochemistry

Double bonds m the mam chain are signaled by the ending enow acid and their position IS designated by a numerical prefix Entries 6 and 7 are representative carboxylic acids that contain double bonds Double bond stereochemistry is specified by using either the cis-trans or the E-Z notation... 

I Ignoring double-bond stereochemistry, what products would you expect from elimination reactions of the following alkyl halides Which will be the major product in each case ... 

Predicting the Double-Bond Stereochemistry of the Product in an E2 Reaction... 

One of the most direct routes to vinylsilanes uses vinyl halides as starting materials. Metal-halogen exchange, followed by electrophilic attack by TMSC1, can often provide the vinylsilane quickly and in good yield. As an added bonus, vinyl bromides have been shown (10, II) to proceed through this sequence with retention of double-bond stereochemistry. 

P212121 Z = 4 Dx = 1.21 R = 0.05 for 1,605 intensities. The carbon chain has a sickle conformation, with C-1-C-2-C-3-C-4, C-2-C-3-C-4-C-5 torsion angles of —60°, -50°, respectively. The dioxolanes have a twist and an envelope conformation, and are related by an approximate, two-fold axis along C-3-C-4. The double-bond stereochemistry is Z. 

Vinylic and divinylic tellnrides react with alkenes in MeOH in the presence of a combination of catalytic amounts of PdCl2 together with AgOAc and EtjN to afford the corresponding vinyl-substituted alkenes The products result respectively from the coupling of the styryl and phenyl moieties of the starting telluride with retention of its double-bond stereochemistry. 

The possibility of nucleophilic attack on different carbons in the resonance-stabilized carbocation facilitates another modification exploited by nature during terpenoid metabolism. This is a change in double-bond stereochemistry in the allylic system. The interconversions of geranyl diphosphate, linalyl diphosphate, and neryl diphosphate provide neat but satisfying examples of the chemistry of simple allylic carbocations. 

Fig. 18. The carboxylaie-histidine-zinc triad represents indirect carboxylate-zinc interaction across bridging histidine. Both tautomers of histidine are observed, and the hydrogen bond stereochemistry with carboxylate (either aspartate or glutamate) is generally syn. Experimental results and theoretical calculations suggest that the carboxylate-histidine- zinc form may be in equilibrium with the carboxylic acid-histidinate- zinc form, as shown.

Fig. 27. Optimal hydrogen bond stereochemistry in the active site of carbonic anhydrase II. Lone electron pairs are represented by stippled dumbbells.

The (Z) and (E) isomers of 4-benzylidene-2-phenyl-5(4//)-oxazolone and 4-(ot-phenylethylidene)-2-phenyl-5(47T)-oxazolone also show different behavior as far as dipole moments are concerned. The solution conformation of the phenyl group relative to the degree of substimtion and double bond stereochemistry has been studied by comparison of experimental and calculated values of dipole moments. ... 

Unactivated dipolarophiles readily participate in intramolecular azomethine ylide cycloadditions with a more reactive azomethine ylide. Thus, flash vacuum pyrolysis of aziridine (113) afforded a 67% yield of the 5,5-fused bicyclic pyrrolidine (Scheme 34).59 A singly stabilized azomethine ylide was the apparent intermediate. Similarly, cyclization of the azomethine ylides derived from (114a-c) gave the corresponding cw-fused 6,6-bicyclic pyrrolidines in 69%, 26% and 16% yield, respectively the original double bond stereochemistry was retained in the latter two cases. 

In a series of studies, Shibasaki examined the formation of chiral benzylic quaternary centers by using asymmetric intramolecular Heck reactions. The effect of double-bond stereochemistry was examined in the cyclization of aryl Inflates 9.1 and 9.3 (Scheme 8G.9) [22], As is commonly... 

In the presence of a catalytic amount of palladium(O), silylated vinyloxiranes (310) have been found to rearrange into a-silylated-/I, y-unsaturated aldehydes (312), not only with complete chirality transfer, but also with total retention of the double bond stereochemistry. A mechanism involving a [l,2]-silicon shift from carbon to carbon via a 7r-allylic palladium complex (311) has been invoked358 for the transformation. New... 

Although the first survey listed 45 natural chlorinated sesquiterpene lactones, several such compounds were omitted in that coverage (1) and are described here. The novel sesquiterpene lactone chlorochrymorin (239) was isolated from Chrysanthemum morfolium (499), and the chlorohydrin graminichlorin (240) is found in Liatris graminifolia (500). The antibacterial AA-57 (241), which is related to pentalenolactone, is produced by a Streptomyces sp. (501). The plant Eupatorium chinense var. simplicifolium has yielded eupachifolin D (242) (502) (side-chain double bond stereochemistry revised (518)), and the new guaianolide andalucin (243) was characterized from Artemisia lanata (503). The previously known chlorohyssopifolins (1) have been studied for cytostatic activity, and the presence of one and even two chlorine atoms amplifies this activity (504). 

The proper double-bond stereochemistry may be achieved by using 2-heptyne as a reactant in the final step. Lithium-ammonia reduction of 2-heptyne gives the trans alkene hydrogenation over Lindlar palladium gives the cis isomer. The first task is therefore the alkylation of propyne to 2-heptyne. 

Other kinds of molecules besides 1 (which has unusual bond stereochemistry) for which these methods might fail to give good results are hypercoordinate molecules like NF5, molecules with noble gas atoms, particularly those of helium and neon, molecules with highly twisted C=C bonds, extraordinarily crowded molecules like hexaphenylethane, unknown dimers, trimers etc. of small familiar molecules, like C202 and N6, and very highly strained molecules. All these cases are discussed in a book on exotic molecules [4],... 

Z)-vinylic tellurides are the source of enynes 212 and enediynes 213 by transformation into vinylcopper species (Section 9.13.8.2.4), followed by reaction with haloalkynes (Scheme 113).278,279 The transformation occurs with retention of the double-bond stereochemistry. This is an efficient and straightforward route to important unsaturated units present in natural products, specially in enediyne antibiotics.280... 

The reaction conditions shown in Scheme 121, but using variable amounts of PdCl2, are used in the construction of a number of unsaturated systems, as shown in Scheme 123.293 297 In all cases, the transformation occurs with retention of the double-bond stereochemistry. 

Procter has recently shown that radical cyclisation-intramolecular aldol sequences can also be carried out.16 For example, treatment of dialdehydes 26 and 27 with Sml2 results in a sequential cyclisation to give 28 and 29, respectively, as single diastereoisomers in high yield (Scheme 6.11). The diastereo-selectivity of the sequence can be ascribed to the chelation of Sm(III) to intermediates, most notably in controlling the double-bond stereochemistry during the formation of Sm(III) enolate 30.16... 

The Syntex chemists reasoned that, if this methyl ketone could be made stereospecifically by fragmenting a cyclic starting material, the (hard-to-control) double bond stereochemistry would derive directly from the (easier-to-control) relative stereochemistry of the cyclic compound. The starting material they chose was a 5/6-fused system, which fragments to give one of the double bonds. 

Bond information includes the bond order, that is, single, double, or triple bond, and bond style, such as simple straight-line bond, wedged bond, dashed bond, wavy bond, broken-line bond, bold bond, and so on. Bond information can also include some special bond types representing the aromatic bonds or bond stereochemistry, for example, wedged or dashed bond. Bond labels are also sometimes found in structures. Different types of bond information are illustrated in Figure 4.2. 

Double bond stereochemistry is encoded using slash (/) and backslash ( ) characters to specify relative positioning of substituents around the plane of a double bond in a manner similar to its common depiction in drawings C C=C C means ( )-butane, and C C=C/C means (Z)-butane. 

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