Heterocyclic analogue

An appreciable amount of information concerning the conformational preferences of substituted heterocycles has accrued, largely through dipole moment and NMR studies. However, the earliest appreciation of this topic apparently arose out of the extension of studies of restricted rotation in biphenyls to heterocyclic analogues. 

The five-membered ring heterocycles possess Diels-Alder reactivity of varying degree. This is most pronounced in the case of furan and benzo[c] fused heterocycles such as isoindole. In this capacity they are functioning as heterocyclic analogues of cyclopentadiene, and high Diels-Alder reactivity can be correlated with low aromaticity. 

As described in Section 1.02.2.3, any heterocycle can be named by indicating (with appropriate prefixes) the positions of heteroatoms in the corresponding carbocycle. The carbocycle can be named systematically, as described in later Sections however, the replacement procedure can also be applied to naming heterocyclic analogues of trivially named carbocycles. A list of polycarbocycles with their trivial names is given in Table 5 (taken from Rule A-21.2 in the lUPAC Blue Book (B-79MI10200)) replacement names may be derived as shown in examples (27) and (28). As demonstrated by example (28), it is unnecessary to add hydro prefixes if the heterocycle cannot accommodate as many double bonds as the original carbocycle. 

As noted in Section 1.02.3.2, replacement procedures can be applied to heterocyclic analogues of polycarbocycles named by fusion nomenclature. Examples (48) and (49) show... 

Substituent effects (electronegativity, configuration) influence these coupling constants in four-, five- and seven-membered ring systems, sometimes reversing the cis-tmns relationship so that other NMR methods of structure elucidation, e.g. NOE difference spectra (see Section 2.3.5), are needed to provide conclusive results. However, the coupling constants of vicinal protons in cyclohexane and its heterocyclic analogues (pyranoses, piperidines) and also in alkenes (Table 2.10) are particularly informative. 

The neutral radical 11.12 is an interesting heterocyclic analogue of 2,2 -bipyridyl. This paramagnetic (spin-bearing) ligand forms an N, -chelated complex with bis(hexafluoroacetylacetonato)cobalt(ir). ... 

These syntheses can be considered as heterocyclic analogue of the poly(ether imide) synthesis... 

The tetracyano derivative of 2.49, 5-diazo-l,2,3,4-tetracyanocyclopentadiene (2.52), and its heterocyclic analogue, 2-diazo-4,5-dicyano-imidazole (2.53) can be obtained by diazotization of the corresponding amines, namely the (anionic) 1-amino-... 

The synthetic method indicated in Scheme 6-38 is important for the preparation of heterocyclic analogues of benzo-l,2,3-triazin-4-ones. The cyclization products of... 

Katritzky et a/.511 have measured rate coefficients for deuteration of 3,5-dimethylphenol and heterocyclic analogues. As in all of the deuteration work of this group, rates of exchange were measured by the nmr method, which is useful for following exchanges at more than one position in the molecule but is, of course, much less accurate than detritiation techniques. In this study, the chemical shift for the ortho and para protons for the parent compound was too small to allow separate integration, but it was apparent that rates of exchange at these two positions did not differ by a factor > 4. From the rate-acidity profile (Table 149) reaction clearly occurs on the neutral species at pD < 3.5 (the log kl versus pD slope was 0.96) and upon the anion at pD > 3.5 (slope zero), and the reactivity of the anion to the neutral molecule was estimated as 107-8, close to the value of 107 noted above. 

In contrast to the series of hydrocarbons, heterocyclic analogues, even of cyclonona-l,4,7-triyne 2 (u = 3), are known. This is because heteroatom linkers more easily adopt smaller bonding angles and thereby provide some relief of overall angle strain. Since heteroatoms have different electronic properties to carbon atoms, the perceived homoconjugative and homoaromatic effects might be expressed more pronouncedly in heterocyclic [n]pericyclines. 

Warshawsky D, T Cody, M Radike, R Reilman, B Schumann, K LaDow, J Schneider (1995) Biotransformation of benzo[a]pyrene and other polycyclic aromatic hydrocarbons and heterocyclic analogues by several green algae and other algal species under gold and white light. Chem-Biol Interact 97 131-148. 

GABA, heterocyclic analogues, 22 (1985) 67 GABAa receptor ligands, 36 (1999) 169 Gas-liquid chromatography and mass spectrometry, 12 (1975) 1 Gastric H /K -ATPase inhibitors, 31 (1994) 233... 

Hepatitis C virus NS3/NS4A protease inhibitors, 44 (2006) 65 Herpes virus, chemotherapy, 23 (1985) 67 Heterocyclic analogues of GABA,... 

This convenient process has been applied to the synthesis of an interesting heterocyclic analogue of j -terphenyl that incorporates three different first-row,... 

The transformation of the cyano group could also introduce a new chiral center under diastereoselective control (Figure 5.13). Grignard-transimination-reduction sequences have been employed in a synthesis of heterocyclic analogues of ephedrine [81]. The preferential formation of erythro-/3-amino alcohols may be explained by preferential hydride attack on the less-hindered face of the intermediate imine [82], and hydrocyanation of the imine would also appear to proceed via the same type of transition state. In the case of a,/3-unsaturated systems, reduction- transimination-reduction may be followed by protection of the /3-amino alcohol to an oxazolidinone, ozonolysis with oxidative workup, and alkali hydrolysis to give a-hydroxy-/3-amino acids [83]. This method has been successfully employed in the synthesis L-threo-sphingosine [84]. 

This hydroxycyclopropanation of a terminal double bond also works perfectly well in an intramolecular situation, e. g. with terminally alkenyl-substituted esters, to yield substituted l-hydroxybicyclo[n.l.O]alkanols [85a,85b,100], aminobicyclo[n.l.O]alkanols [85c], and heterocyclic analogues [99a,99b,100], in which five- and six-membered rings are formed (Table 11.7). 

Heterocyclic analogues of diarylmethane dyes in which the central carbon atom has been... 

In general, ketones, alcohols and ethers of formula (3) showed comparable protection against cisplatin-induced emesis in the dog and ferret with that of metoclopramide. Erythro (cis) alcohols (3c, 3g, 3i) were found to be more potent than the corresponding threo-(trans) isomers (3d, 3h, 3j). Optical isomer (.R) (3e) was found to be somewhat more potent than its (S )-enantiomer (3f) as an antagonist of cisplatin-induced emesis in the ferret. In the dog, both isomers showed similar activity. A number of heterocyclic analogues were also studied but with the exception of (3k), all were inferior in potency as antiemetic agents compared with other compounds (3) shown in Table 7.1. Lead compound, BMY 25801, batanopride, (3a) is presently under clinical investigation. 

GABA, heterocyclic analogues, 22 (1985) 67 Gas-liquid chromatography and mass spectrometry, 12 (1975) 1... 

Borepin is the heterocyclic analogue of the tropyl-ium cation with a jr-electron sextet. Few borepin derivatives have been reported a monocyclic 1-meth-ylborepin 202,245 benzo derivatives 204,246 and a dithienoborepin 205247 (Scheme 77). Heptaphenyl-... 

Unsaturated lactone 74 (Scheme 7.21) can be viewed as an oxygen heterocyclic analogue of 2-cyclohexenone, and it has recently been reported that catalytic 1,4-additions of Et2Zn to 74 can indeed be accomplished with high enantioselectivity. For adduct 76, Reetz achieved a remarkable 98% ee when employing ferrocene-based diphosphonate ligand 23 [48]. Using diphosphite 24, Chan et al. achieved an ee of 92% for the six-membered lactone 74 and a 56% ee for the five-membered lactone 25 [49c]. 

Comparison of Basicity of Some Heterocyclic Analogues of Chromone,... 

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