Ethano-bridged derivative

In a subsequent calculational study [HF and MP2 levels of theory with 6-31G(d) basis set and MP4(SDQ)], Szabo and Cremer849 explored the he C7Hn+ potential energy surface. Cation 487 (tricyclo[4.1,0.01,3]heptyl cation), the protonated ethano-bridged derivative of spirocyclopentyl cation, was considered to be the missing link between the bicyclo[3.2.0]hept-3-yl cation 488 and the 7-norbomyl cation 489. It is a kinetically stabilized species separated from cations 488 and 489 by 18.9 and 15.9 kcal mol-1, respectively. 

In recent years further novel classes of compounds were added to cyclophane chemistry. The multilayeredphanesiS derived from [2.2]paracyclophane contain coaxially stacked benzene rings connected by ethano bridges para to one another. The first members of this series were described in 196416. Quadruple layered phane hydrocarbons 3 and 4 reveal in their UV-spectra long range electronic effects penetrating several arene units. 

At first, reaction of 1,2-dibromethane with an excess of indcnyl magnesium bromide leads to the ethano-bridged bis-tetrahydroindenyl ligand 32 (mixture of isomers), from which the racemic complex (rac-31) is obtained. The separation of the enantiomers is finally achieved by fractionated crystallization of the derivative 33 (R OH = (R)-O-acetylmandelic acid). 

Another system which is not usually considered as a 2-bicyclo[2.1.0]pentyl system but in reality is a 3,5-ethano bridged endo derivative is the tricyclo[2.2.1.0 ]hept-2-yl p-nitrobenzoate (55) shown below " . This is related to the anti-7-norbornenyl system by... 

The next attempt at these reactions were carried out by Yamamoto et al. [26], They coupled 2,7-dibromo-9,10-dihydrophenanthrene to give an ethano-bridged poly(p-phenylene) derivative [poly(9,10-dihydrophenanthrene-2,7-diyl)] (9) by way of low-valent nickel complexes, which were used either stoichiometrically as reagent (Ni(COD)2) or were generated electrochemically in the reaction mixture. As a result of the insufficient solubilization of the ethano substituents only the oligomer fraction with Mn<1000 is soluble, the polymeric products precipitating out as an insoluble powder. The value of for the soluble fraction of 9 is about 360 nm. 

Ahyd was measured in acetic acid solution. Solvent effects are significant for the alkenes and may cause the measured enthalpy changes to be 0.7 kcal mol 1 less exothermic than the gas-phase values. Interest in this and the following dimethanonaphthalene derivatives arises from their enthalpies of partial hydrogenation which is, sequentially, -34.1 and -26.9 kcal mol 1. The unusually small value of Ahyd7/ for the second step is indicative of repulsion between the ethano bridges in the tetracyclo[4.4.1.1. OJdodecane produced. 

The bridgehead diolefins 210 and 211, which, like 55, are formally alkylene-bridged derivatives of trans, frans-cycloalkenes, have been reported (165) (Scheme 10). The stability of 211 toward heat, air, and moisture is in contrast to that of the unsubstituted bicyclo[4.2.2]deca-1,5-diene (210). The latter diene was obtained by a kinetically controlled reductive deiodination of 209, which leads to the cleavage of the cyclobutano bridge in preference to the ethano bridge, despite the greater thermodynamic stability of the monocyclic diene to be expected from the latter reaction. 

Recent interest has been shown by SKF in the bio-activity of an analogue of androstenedione (17). A derivative of (17) was synthesized with an ethano bridge between the axial 10 and 2 positions (100). This bridge was demonstrated, by X-ray analysis, to alter considerably the conformation of the steroid A-ring and the 19-carbon leaned towards the centre of the A-ring as compared with (17). The biological data for this compound are to be reported in the near future [215]. 

Dihydropyrenes are specific examples of ethano-bridged [14]annulenes. Most of the studies on these compounds have involved those having the groups attached to the bridging atoms on opposite sites of the ring system, i.e, treats derivatives ... 

Another procedure to yield ethano-bridged 1,3-butadiynes was used by Scott et al. to prepare octamethylcyclododeca-l,3,7,9-tetrayne (17) (Scheme 7.5) [36]. This group found that in situ generated tetramethylhexapentaene (16) could be dimerized to 17 by Cu(i) catalysis. Similarly the related hexapentaene derivative 18 yielded in such a cycloaddition process the head-to-head dimer 19 [37a]. 

Hamada and Mukai synthesized the ethano-TB analog 79 via the reaction of 1 and its methoxy derivative 80 with 1,2-dibromethane (Scheme 18). The endomethylene bridge was converted into endoethylene in greater than 70% yield (96TA2671). 

---