Trans-Di

The common names of these alkenes are c/s and trans di tert butylethylene In cases such as this the common names are somewhat more convenient than the lUPAC names because they are more readily associated with molecular structure... 

A chiral titanium complex with 3-cinnamoyl-l,3-oxazolidin-2-one was isolated by Jagensen et al. from a mixture of TiCl 2(0-i-Pr)2 with (2R,31 )-2,3-0-isopropyli-dene-l,l,4,4-tetraphenyl-l,2,3,4-butanetetrol, which is an isopropylidene acetal analog of Narasaka s TADDOL [48]. The structure of this complex was determined by X-ray structure analysis. It has the isopropylidene diol and the cinnamoyloxazolidi-none in the equatorial plane, with the two chloride ligands in apical (trans) position as depicted in the structure A, It seems from this structure that a pseudo-axial phenyl group of the chiral ligand seems to block one face of the coordinated cinnamoyloxazolidinone. On the other hand, after an NMR study of the complex in solution, Di Mare et al, and Seebach et al, reported that the above trans di-chloro complex A is a major component in the solution but went on to propose another minor complex B, with the two chlorides cis to each other, as the most reactive intermediate in this chiral titanium-catalyzed reaction [41b, 49], It has not yet been clearly confirmed whether or not the trans and/or the cis complex are real reactive intermediates (Scheme 1.60). 

A salient structural feature of intermediate 18 (Scheme 2b), the retrosynthetic precursor of aldehyde 13, is its y,r5-unsaturated ester moiety. As it turns out, the Johnson ortho ester variant of the Clai-sen rearrangement is an excellent method for the synthesis of y,<5-unsaturated esters.11 In fact, the Claisen rearrangement, its many variants included, is particularly valuable in organic synthesis as a method for the stereocontrolled construction of trans di- and tri-substituted carbon-carbon double bonds.12,13 Thus, it is conceivable that intermediate 18 could be fashioned in one step from allylic alcohol 20 through a Johnson ortho ester Claisen rearrangement. In... 

Metalated epoxides can react with organometallics to give olefins after elimination of dimetal oxide, a process often referred to as reductive alkylation (Path B, Scheme 5.2). Crandall and Lin first described this reaction in their seminal paper in 1967 treatment of tert-butyloxirane 106 with 3 equiv. of tert-butyllithium, for example, gave trans-di-tert-butylethylene 110 in 64% yield (Scheme 5.23), Stating that this reaction should have some synthetic potential , [36] they proposed a reaction pathway in which tert-butyllithium reacted with a-lithiooxycarbene 108 to generate dianion 109 and thence olefin 110 upon elimination of dilithium oxide. The epoxide has, in effect, acted as a vinyl cation equivalent. 

All attempts to oxidize either cis- or trans-di-t-butylthiirane oxides failed122 (see equation 20). Reagents investigated included m-chloroperbenzoic acid, sodium peroxide, hydrogen peroxide, ozone and aqueous potassium permanganate. The cis oxide was resistant to oxidation (apparently steric hindrance), and the trans isomer was consumed with excess oxidizing agent but no identifiable products could be isolated. 

This process is both stereoselective and stereospecific. When applicable, a trans di-substituted alkene will be favored over a cis disubsti-tuted alkene. 

Twenty years later, by studying the chlorination of cis- and trans-di-t-butylethylenes, Fahey (1966) showed that halogen bridging is a general rule. It is expected that, owing to steric repulsions between the two branched groups, the cis-alkene would prefer to react via an open / -chlorocarbocation [14] where free rotation can occur rather than via a chloronium ion [15]. 

Asymmetric osmylation of alkenes.3 In the presence of 1 equiv. each of 1 and 0s04, alkenes undergo highly enantioselective ris-dihydroxylation. Highest enantiofacial selectivity (90-99%) is shown in osmylation of trans-di- and trisub-... 

Dibutyl hyponitrite, 3069 trans- Di-fe/7-butyl hyponitrite, 3070 Diethyl hyponitrite, 1690 Diisopropyl hyponitrite, 2538 Dimethyl hyponitrite, 0913... 

Several factors can influence the effectiveness of a metal scavenger, one of which is the oxidation state of the metal. In these studies the removal of Pd(II) as trans-di( j-acetato) bis [o-(di-o-tolylphosphino) benzyl] dipalladium (II) (3) and Pd(0) as tetrakis-(triphenylphosphine)palladium(0) (4) was investigated. 

Ligand variation has resulted in considerable improvement of the reaction s efficiency (Scheme 38). With 9-0-(9 -phenanthryl) (PHN) ethers and 9-0-(4 -methyl-2 -quinolyl) (MEQ) ethers of dihydroquini-dine and dihydroquinine as ligands, olefins of various substitution patterns, mono-, gem-di-, trans-di-, and certain trisubstituted substrates can be dihydroxylated with high enantioselectivity (89). Some examples of these reactions are given in Scheme 38. The reaction occurs at either ambient or ice-bath temperature with the solid, nonvolatile Os(IV) salt, K20s02(0H)4, instead of 0s04. The substrate/catalyst ratio for this reaction is 2000 for terminal olefins. 

Wasserheit, N.J. 1992. Epidemiological synergy Interrelationships between HIV and infection and other STDs. Sex Trans Dis 19 61. 

Judson. F.N., et al. 1989. In vitro evaluation of condoms with and without nonoxynol-9 as physical and chemical barriers against Chlamydia trachomatis, herpes simplex virus type 2, and human immunodeficiency virus. Sex Trans Dis 16 51. 

A number of papers describe the synthesis of thietane rings starting from thiirane rings. Lucchini et al. studied the different reactivities of cis and trans di-fert-butylthiiranium ions, 96a and 96b, with water <1997JOC7018>. It was demonstrated that the reaction of cis di-fert-butylthiiranium ion 96a with water led first to the formation of an open-chain alcohol 97, which, after ring closure, formed the trans di-/r y-butylthiiranium ion 96b. The trans Ai-tert-butylthiiranium ion 96b then rearranged to the thietanium ion 98 (Equation 31). 

In the two cis/trans isomers of 4-chlorocyclohexane carboxylic acid the conformers with axial chloro atoms have conformational energies ca. 30% below those with equatorial chloro atoms (99MI7) in this connection the proportion of the trans-di-axial conformer is greater than expected. 

Just as there are substances with the same empirical formula that differ in their molecular formula, there are substances that have the same empirical and molecular formula. The only way to differentiate these substances is by determining the structural formula for each substance. For example, Cis dibromoethene and Trans di-bromoethene have the same empirical formula (CHBr) and the same molecular formula ( 2112 2) must be distinguished by a unique structural formula. 

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