Ring substitution, angular

The applied Gould-Jacobs reaction is very often used to prepare angularly annelated pyridine-ring-substituted imidazoquinolines in inert media under conditions of thermal cyclocondensation, for example at temperatures above 250°C. 

Chung and coworkers [280] combined a [2+2+1] with a [2+2+2] cycloaddihon for the synthesis of multi-ring skeletons, angular triquinanes, and fenestranes. For the preparation of tetracyclic compounds such a 6/4-17, these authors used diynes as 6/4-16 and CO as substrates (Scheme 6/4.5). Fully substituted alkynes gave low yields, and 1,5- as well as 1,7-dialkynes, did not react... 

Similar aromatic ring-substitution effects on conformational equilibria to those shown by 216 are shown by the dibenzo[a,/]quinolizidines (221). Examples are provided by 29 and 30,51 described in Section II,B,1. In these systems Jgem and angular proton shifts are sensitive to aromatic ring-orbital-nitrogen lone-pair overlap (Sections II,B,1 and 2). 

In small rings the angular strain is sufficiently high to compensate the conformational strain in the macromolecule. Thus, even fully substituted oxiranes can polymerize. Cationic polymerization of 1,1,2,2-tetramethyloxirane is a good example of this countereffect ... 

One synthetic approach involves cyclization of a substituted six-membered heterocycle which becomes the central ring of the product (6 6 6). For example, the reaction of 2,6-diaminopyridine with 2,2-dimethyl-l,3-dioxane-4,6-dione and trimethoxymethane gives the bis-adduct 118 which is a precursor to the angular tricyclic product 119 (Scheme 14) <2005AXCol>. 

The thermal cyclization of m-phenylenediamine derivatives (799) by heating in diphenyl ether afforded angular l,7-phenanthroline-3,9-dicarboxylate (800), if a substituent was not present at position 2 of the phenyl ring of 799 (R = H), but the linear pyrido[3,2-g]quinolinecarbox-ylate (801, R = Me, R1 = R2 = H) was prepared from the 2-methyl-substituted derivative (799, R = Me, R1 = R2 = H) (72GEP2220294). 

The values in Table 23 show that in unsubstituted benz[a]anthracene the ion A has the greater basicity. On substitution of the angular ring, the basicity increase is approximately equal. Ion A is favoured for substituents in the vicinity of the 7-position (positions 5, 6, 8, 9), and ion B is favomred by substituents in the vicinity of the C-atom 12 (10... 

---