Ethano bridge

A series of patents from Sobering AG has described the synthesis of various 14—17 a- and P-ethano-bridged estratriene compounds represented by... 

The ethano bridge in some 1,4-ethanoquinoxalines may be displaced from one ring nitrogen to furnish A(-(substimted ethyl) hydroquinoxalines. Several aspects of this fundamental reaction are illustrated in the following examples. 

Because of the better jt-type overlapping of the carbonyl jt orbital with the o bonds of the ethano bridge as compared with that of the methano bridge in 27 (i.e., 9 (dihedral angle, or ZCfff. ) < 9 (dihedral angle or... 

The HOMOs of unsubstituted vinylidenenorbomane 47a and unsubstituted bicyclo[2.2.2]octene 48a are intrinsically comprised of similar components, i.e., the n orbital of the ethylene and the o-orbitals of the ethano bridges, the coupling being in an out-of-phase fashion (50 and 51), though the arrangement of the components is different. The contour plot (49) of the HOMO of 48a is consistent with these orbital interactions (50). 

A direct connection between the allene group and another unsaturated functional group is no prerequisite for interesting chemical behavior, as illustrated for hydrocarbons 28-31 in Scheme 5.3, in which the allene unit and the above four substituents are connected either by a methylene group or by an ethano bridge, as for allenes 32-35. 

Compound 99 was obtained on a preparative scale by reaction of 2,6-bis(bromomethyl)pyridine (102) with phenyllithium, but attempts to introduce functional groups in the ethano-bridge were unsuccessful.117 Compound 100 has been prepared via the transformation of sulfide linkages to carbon-carbon double bonds (Scheme 6). 

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. 

The ethano-bridged analog 611 was also prepared from the 8-chloroticyclo [3.2.1,02,4]octane precursor.1063 Ion 611 closely resembles the trishomoaromatic ion 610 in its spectral properties. 

In contrast to these results, the mass spectral fragmentation of cavinine (372) was suggested to be governed by the epoxide ring at C-l and C-2 rather than by the hydroxyl group at C-l 1 on the ethano bridge. This conjecture was based on the observation that the base peak corresponded to the loss of the CHO of the... 

Figure 36. (a) Absolute configuration and exciton chirality of an ethano-bridged 1,1 -bianthryl. (b) Absolute configuration and exciton chirality of (-)-2,2 -bis-(bromomethyl)-l,l -binaphthyl. 

Scheme 4.3 Antibody 39-All catalyzes a Diels—Alder reaction between an electron-rich acyclic diene (8) and an N-aryl maleimide (9). It was elicited with the bicyclo[2.2.2]octene hapten 7. The ethano bridge locks the cyclohexene ringintothe requisite boat conformation but has no counterpart in the substrates or transition state.

The substituted [2.2]paracyclophanes prepared by the present procedure have proven to be useful starting materials for the synthesis of cyclophanes with extended aromatic ring systems,16 additional ethano bridges,17-18 and chromium tricarbonyl complexes.19... 

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. 

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