E-stereochemistry

IUPAC (1976) Rules for the Nomenclature of Organic Chemistry. Sect. E Stereochemistry. Pure Appl. Chem. 45, 11 [1.2]... 

Noteworthy features of these reactions are the high predominance of E stereochemistry in the case of aldehydes and the good results obtained even with highly enolizable ketones (such as cyclopentanone), a, -epoxy ketones (isophorone oxide) and a,j8-unsaturated compounds (benzalacetophenone and cinnamaldehyde). 

From our discussions of bonding, we have learnt something about the arrangement of bonds around various atoms (see Chapter 2). These concepts are fundamental to our appreciation of the shape of molecules, i.e. stereochemistry. Before we delve into these matters, let us recap a little on the disposition of bonds around carbon. 

Eliel, E. E. Stereochemistry of Carbon Compounds. New York-San Francisco-Toronto-London McGraw-HiU 1962. 

There have been three reports of the same dimeric disulfide. It was first isolated from an unidentified sponge from Guam and the structure elucidated by analysis of spectral data. The (E,E) stereochemistry of the disulfide (500) was defined by comparing the I3C NMR spectroscopic data with those of the (E,Z)-isomer (501) that was obtained as an unstable minor product [425]. Compound 500 was isolated from a species of Psammaplysilla and was called psammaplin A [426]. It was also isolated from Thorectopsamma xana, collected from the same location in Guam, together with a minor dimeric metabolite bisaprasin (502). Both compounds inhibited growth of Staphylococcus aureus and Bacillus subtilis [427]. Psammaplin A (bisprasin) (500) was later isolated from a Dysidea species of sponge and shown to act on Ca2+-induced Ca2+ release channels of skeletal muscle [428]. 

Juaristi, E., Stereochemistry and Conformational Analysis, Wiley-Interscience, New York, 1991. 

Copper(I) salts of enamines have been allylated with the 2-allyloxybenzimidazoles to give y,5-unsaturated ketones upon hydrolysis (79CL957). Primary allylic ethers react preferentially at their a-carbon with retention of double bond configuration whereas secondary allylic ethers react mainly at the y-carbon to afford alkenes of predominantly (E)-stereochemistry. 

The relatively constant kinetic disadvantage experienced by an average vinylcyclopropane rearrangement, compared with a (kt + k2) stereomutation, amounts to a A A (7 of about 3 kcal moT1. This may well be associated with configurationally distinct sets of diradical structures with those of E stereochemistry favored thermodynamically over those of Z stereochemistry by about 3 kcal mol 1. Only the latter may lead to cyclopentene products212. 

By inspection one can see that the the 2R,3S and 2S,3R isomers are enantiomers and the 2R,3R and 2S,3S pair are enantiomers. As they are drawn, one can see the original E stereochemistry of the double bond. Thus the first pair comes from a stereospecific trans addition across the double bond while the second pair comes from a stereospecific cis addition. Clearly the stereochemistry of the double bond is maintained throughout the addition. Since iodine is the electrophile, a bridged iodonium ion is likely responsible. The initial addition gives only a single pair of enantiomers since the only nucleophile is benzoate. Also noted is that iodine is not in the product so something must replace the iodine. The silver ion would help to remove the iodine. Since iodine would cause a trans addition and the product has oxygens added trans, there must be a replacement of iodine by an... 

The range of monoterpenes encountered is extended considerably by cyclization reactions, and monocyclic or bicyclic systems can be created. Some of the more important examples of these ring systems are shown in Figure 5.11. Such cyclizations would not be expected to occur with the precursor geranyl diphosphate, the E stereochemistry of the double bond being unfavourable for ring formation (Figure 5.9). Neryl PP or linalyl PP, however, do have favourable stereochemistry, and either or both... 

The synthesis of 9-alkenyl-9-BBN via hydroboration of terminal alkynes with 9-BBN suffered from the formation of 1,1-diborylalkanes via dihydroboration along with desired monohydroboration products. Alternatively, selective monohydroboration of terminal alkynes with dicyclohexylborane was followed by transmetallation with 9-MeO-9-BBN (Equation (193)).710 Treatment of the hydroboration intermediates with DIBAL-H in the presence of a borane-trapping reagent such as 1-hexene gave 1-alkenylaluminum compounds with complete retention of the (E)-stereochemistry (Equation (194)).711... 

Dunitz, J. D., and Orgel, L. E. Stereochemistry of Ionic Solids, in Emeleus and Sharpe s Advances in Inorganic Chemistry and Radiochemistry, Yol II, 1-60, Academic Press Inc., New York (1960). 

AcfdttyandbasicItycti8, % Carbonyl chemistry Ctil2 chi e Stereochemistry ch 6 ConformatlonalanatysischlS... 

When R = Ph, Me3Si, 52 is the main product obtained by deprotonation by conditions (a) or (b). When R = Me, 52 is obtained in 95% yield by deprotonation conditions (a), and 53 is obtained under deprotonation conditions (b). When propionaldehyde is bound to a chiral analog of 52, the stereoselectivity is especially high under conditions (a), the structure equivalent to 52 is obtained in a yield higher than 98% with E stereochemistry between carbons and C2 and Z stereochemistry at the —N bond,... 

The hydrosilation of 1-alkynes can give either Z-or E-isomers (see (E) (Z) Isomers) of the linear vinylsilane or the Markownikow product (equation 5). Reaction of 1-hexyne with trichlorosilane under platinum catalysis conditions gives a mixture of 1- and 2-silyl-l-hexene (78 22). From the E-stereochemistry of the 1-silyl isomer, a yyn-addition mechanism can be assumed. 

Ohloff G, Vial C, Wolf HR, Job K, Jegou E, Polonsky J, Lederer E.. Stereochemistry—odor relationships in enantiomeric ambergris fragrances. Helv. Chim. Acta. 1980 63 1932-1946. 

The pure E stereochemistry of the vinylsilane 21 clearly shows that the carbocylization proceeds in a totally stereoselective fashion to give, under these conditions (20 °C, 5 min) the configurationally stable (Z)-alkenylzinc bromide [21] 20 via a syn addition of the allenic zinc bromide to the acetylenic moiety. This carbocyclization represents a new desymmetrization of diynes such as 18 which serves to deliver functionalized exo-... 

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