Carbon-bridged system

Bridging alkylidene complexes similarly react with alkynes to afford isolatable derivatives arising from the formal insertion into one metal-carbon bond. So, UV irradiation of M2(CO)2(/t-CO)( U-CHCH3)(>j -Cp), in the presence of acetylene results in the fomation of a new carbene and a three-carbon bridging system, XXII ... 

Antidepressant activity is retained when the two carbon bridge in imipramine is replaced by a larger, more complex, function. Nucleophilic aromatic substitution on chloropyridine 31 by means of p-aminobenzophenone (32) gives the bicyclic intermediate 33. Reduction of the nitro group (34), followed by intramolecular Schiff base formation gives the required heterocyclic ring system 35. Alkylation of the anion from 35 with l-dimethylamino-3-chloropropane leads to tampramine 36 [8]. 

The dipyrrylacelylenedicarbaldehyde 18, which already contains, along with the acetylene moiety, two of the two-carbon bridges of the final macrotetracycle, can be prepared by a Heck-type coupling of 5-iodopyrrole-2-carbaldehydes with acetylene.8a,b The main conjugation pathway with 22n electrons is already present in the acetylene-cumulate systems 19. The expected planarity of this chromophore has been confirmed by X-ray structure analysis.8a b... 

SYSTEMS WITH UNUSUAL STRUCTURAL FEATURES QUATERNARY CARBON ATOMS, MEDIUM-SIZED RINGS AND BRIDGED SYSTEMS... 

Up to now, we have seen how the "heuristic principles" can be applied to both linear and cyclic systems which we could call "normal systems". When some unusual structural features -such as quaternary carbon atoms, medium-sized rings or bridged systems- are found in the molecular structure under consideration, one may assume that they are derived either from a rearrangement or from an internal fragmentation [1]. 

UNUSUAL SYSTEMS quaternary carbon atoms, medium-sized rings (from 7 to 10 atoms) and bridged systems ... 

The chemistry of the bicyclo[2.2.1]heptane ring system, with and without double bonds in the two-carbon bridges, includes many well-known and interesting features which illustrate important stereochemical aspects of some organic reaction mechanisms. Among derivatives of... 

The alcohol portion in hyoscyamine is tropine in hyoscine it is the epoxide scopine. Tropine is an example of an azabicyclo[3,2,l]octane system with a nitrogen bridge, whereas scopine is a tricylic system with a three-membered epoxide ring fused onto tropine. Note that systematic nomenclature considers an all-carbon ring system with one carbon replaced by nitrogen hence, tropane is an azabicyclooctane (see Section 1.4). 

We thus start with the smallest and simplest systems for which we have thermochemical data, the isomeric 2- and 7-bicyclo[2.2.1]heptanones (the norbomanones, 39a and 39b). Our intuition suggests that the latter species is more strained since the increased geometric constraints of a single-carbon bridge over those for a two-carbon bridge are... 

Alkyl spacers thus offer the opportunity to finely tune the interplay between the antagonist sites of ambiphilic compounds. The proximity of the phosphine and borane moieties, and thus the possible formation of intramolecular P-B interaction depend on the number of carbon atoms present in the backbone and on the Lewis acidity of the borane. Conformational considerations may also play an important role as for the ethylene-bridged systems. 

Corrole is a tetrapyrrolic macrocycle with a direct link between two pyrrole rings. Lacking a C-20 meso carbon bridge it has a corrin like skeleton with double bonds involving porphyrin-like conjugation. It has an 18 electron rt system and hence aromatic character. The direct link between the A and D... 

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