Stereoisomers aromatics

The steric bulk of the three iodine atoms in the 2,4,6-triiodoben2ene system and the amide nature of the 1,3,5-substituents yield rotational isomers of the 5-A/-acyl-substituted 2,4,6-triiodoisophthalamides. Rotational motion in the bonds connecting the side chains and the aromatic ring is restricted. These compounds also exhibit stereoisomerism when chiral carbon atoms are present on side chains. (R,5)-3-Amino-l,2-propanediol is incorporated in the synthesis of iohexol (11) and ioversol (12) and an (3)-2-hydroxypropanoyl group is used in the synthesis of iopamidol (10). Consequendy, the resulting products contain a mixture of stereoisomers, ie, meso-isomers, or an optical isomer. 

HMD was originally produced by Du Pont as a coproduct in the manufacture of Qiana fiber. Du Pont subsequently sold the product to Bayer. In the 1990s MDA is hydrogenated by Air Products for Bayer (see Amines, aromatic-methylenedianiline). Commercial HMDI is a mixture of three stereoisomers. Semicommercial aUphatic diisocyanates include /n j -cyclohexane-l,4-diisocyanate (CHDI) and y -tetramethylxylylene diisocyanate (TMXDI). A coproduct in the production of TMXDI is y -isopropenyl-a,a-dimethylben2yl isocyanate (TMI), which can be copolymerized with other olefins to give aUphatic polyisocyanates. 

Saturation of the aromatic ring of pentopril analogues is also consistent with ACE inhibition as demonstrated by the oral activity of indolapril (23). The necessary heterocyclic component (21) can in principle be prepared by catalytic perhydrogenation (Rh/C, HOAc) of the corresponding indole. A single isomer predominates. The product is condensed by amide bond formation with the appropriate alanylhomophenylalanyl dipeptide ester 20 to give 22. Selective saponification to 23 could be accomplished by treatment with HCl gas. Use of the appropriate stereoisomers (prepared by resolution processes) produces chiral indolapril [8]. 

Only one example, showing high stereoselectivity, is known in this class of reactions. On treatment of the acyclic glycine cation equivalent 1 (see Appendix), containing the ( + )-cam-phor-10-sulfonamide ester as a chiral auxiliary, with boron trifluoridc and anisole at 0"C a mixture of aromatic substitution products is obtained in essentially quantitative yield 55. Besides 11 % of cuV/io-substitution product, the mixture contains (R,S)-2 and its (/ ,/ )-epimer in a ratio >96 4 (NMR). The same stereoisomer 2 predominates when the reaction is conducted in sulfuric acid/acetic acid 1 9, although the selectivity is slightly lower (91 9 besides 25% of ortho substitution). 

The copper-catalyzed 1 1 additions of aliphatic and aromatic sulfonyl chlorides82,85 or bromides84 to acetylenes yielding mixtures of trans- and cis-/3-halovinyl sulfones have also been described. Highly polar solvents favored trans addition, while cis addition predominated in low polarity media84,85. A comparison between the thermal and the copper-catalyzed addition of sulfonyl bromides to phenylacetylene (cf. Scheme 6) enabled Amiel84 to suggest that the two stereoisomers do not have a common intermediate. That is, the trans addition product is a result of a normal radical chain, while the cis addition... 

The reaction of metabolically generated polycyclic aromatic diol epoxides with DNA Ua vivo is believed to be an important and critical event in chemical carcinogenesis Cl,2). In recent years, much attention has been devoted to studies of diol epoxide-nucleic acid interactions in aqueous model systems. The most widely studied reactive intermediate is benzo(a)pyrene-7,8-diol-9,10-epoxide (BaPDE), which is the ultimate biologically active metabolite of the well known and ubiquitous environmental pollutant benzo(a)pyrene. There are four different stereoisomers of BaPDE (Figure 1) which are characterized by differences in biological activities, and reactivities with DNA (2-4). In this review, emphasis is placed on studies of reaction mechanisms of BPDE and related compounds with DNA, and the structures of the adducts formed. 

Only the Schiff bases of aromatic aldehydes took part in the reaction. When R1 = CH3, the piperidone was obtained as a mixture of stereoisomers in 73% yield at 80°C for 10 hours. 

The tetra-bridged phosphatocavitands lOa-j (Scheme 11) were obtained by reaction of the corresponding resorc[4]arene with R0P(0)Cl2 (R=aromatic or alkyl group) in acetone in presence of triethylamine as base. In most cases, several isomers due to the different orientation of the P=0 bonds were formed in variable amounts, whereas the iiii and 0000 stereoisomers were not, or only in trace amounts [58-62]. Usually, the iiio isomer is the most abundant compound and the strereoselectivity of the reaction was essentially attributed to the preference of the host molecule to fill the cavity with at... 

The term oxime dates to the 19th century, a combination of the words oxygen and imide. Oximes exist as two stereoisomers syn (Z) and anti (E). Aldoximes, except for aromatic aldoximes, exist for the most part as the syn isomer, while ketoximes are obtained as both syn and anti isomers, which can be separated almost completely. Recently, Kolandaivel and Senthilkumar have studied the molecular structure and conformational stability of anti and syn conformers of some aliphatic aldoximes by employing the ab initio and density funetional theory (DFT) methods. 

The Diels-Alder reaction of (Z)-4-arylidene-2-phenyl-5(4//)-oxazolone 707 and Danishefsky s diene is best conducted in toluene at reflux to produce both the endo and the exo stereoisomers of 708. Base treatment of the cycloadduct mixture promotes aromatization through spontaneous oxidative decarboxylation to give 3-aryl-4-benzamidophenols that are converted to 3-aryl-4-aminophenols 709 by acid... 

Most local anesthetic agents consist of a lipophilic group (eg, an aromatic ring) connected by an intermediate chain via an ester or amide to an ionizable group (eg, a tertiary amine) (Table 26-1). In addition to the general physical properties of the molecules, specific stereochemical configurations are associated with differences in the potency of stereoisomers (eg, levobupivacaine, ropivacaine). Because ester links are more prone to hydrolysis than amide links, esters usually have a shorter duration of action. 

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