Trans effect selective synthesis

An important application of the trans effect is the synthesis of specific isomers of coordination compounds. Equations (3) and (4) show how the cis and trans isomers of Pt(NH3)2Cl2 can be prepared selectively by taking advantage of the trans effect order Cl > NH3. This example is also of practical interest because the cis isomer is an important antitumor drug, but the trans isomer is ineffective. In each case the first step of the substitution can give only one isomer. In equation (3) the cis isomer is formed in the second step because the Cl trans to Cl is more labile than the Cl trans to the lower trans effect ligand, ammonia. On the other hand, in equation (4) the first Cl to substitute labilizes the ammonia trans to itself to give the trans dichloride as final product. 

Trans Effect in Selective Synthesis of cis and trans Dichlorodiammineplatinum(II)... 

Long chain 2-alkyl-l-(2-hydroxyethyl)-2-rmidazolmes (at 150 °C) and their amide precursors at 120 °C were readily obtained by condensation of aminomethy-lethanolamine with fatty acids using CaO as inorganic support [170]. A non-thermal effect is implicated. A one-pot selective synthesis of ds- and trans-2,4,5-triarylimidazolines from aromatic aldehydes was achieved under irradiation conditions via methadiamines and selected bases [171]. 

A Dieckmann reaction of 7 and enol etherification provided trans-octalone 6 in 90% yield. An additional 10% of the transposed /3-ethoxy -enone 24 was also isolated. Compound 24 could easily be removed chromatographically (the first chromatography of the synthesis) and could be isomerized back to the 9 1 mixture in favor of 6 by resubjection to the etherification conditions. Compound 7 had three different CC Et groups, yet only the one adjacent to the CN group was attacked by the nascent ketone enolate. This selectivity, attributed to the effect of the powerfully electron-withdrawing CN group, was expected, as it was observed previously in the preparation of 3c.3 The selectivity of the enol ether formation was also expected from previous work. 

It is possible that cisplatin cytotoxicity arises from more subtle effects than just general inhibition of transcription. The expression of some genes with a strong promoter is inhibited more in cultured cells by cisplatin than bulk RNA synthesis, and this differential sensitivity was not observed for trans-DDP [157][158], On the other hand, the induction of several weak promoters by cisplatin is reminiscent of the bacterial SOS response [158] [159]. Since the inhibition or activation of RNA polymerase II-medi-ated transcription by cisplatin is gene-specific and modulated by the promoter region, the end result would not be to shut down the cellular machinery so much as to create an imbalance. The selective inhibition, or induction, of gene expression by cisplatin is particularly relevant with respect to the expression of oncogenes, several of which have been implicated in cisplatin resistance [25],... 

Comparable cis/trans selectivities and similar conformational effects on them were studied in ring enlargements of cyclic sulfonium ylides. ° Rearrangements of sulfur ylides performed in repetition were used for stepwise ring expansion 5- 8—> 11- —> 14- - 17-membered. ° Synthesis applications of... 

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