Bridging strategies

Other types of bridged strategy were developed with promise. For example, Ziegler [149,150] reported the use of a diester linker that connected the donor and the acceptor components (O Scheme 48). A related strategy was developed by Schmidt [151]. 

Klaassen Lijnse, 1996, for further discussion, including an evaluation of the bridging strategy of Clement et al, 1989). 

Define bridging strategy Teratology studies 2nd species Answer specific questions... 

Final formulation Local tolerance Bridging strategy... 

Synthesis of cryptands which contain nitrogen atoms in the bridges has also attracted Lehn s attention. In general, a similar synthetic strategy was utilized, but ni-... 

As attractive as the transannular bridging of bis(thiolactones) to bicyclic bis(oxepane) frameworks is, our inability to convert the disulfide bridging product (see 25, Scheme 5) to a mmv-fused bre-vetoxin-type bis(oxepane) (see 28) necessitated the development of a modified, stepwise strategy. This new stepwise approach actually comprises two very effective methods for the construction of cyclic ethers the first of these is the intramolecular photo-induced coupling of dithioesters, and the second is the reductive cyclization of hydroxy ketones. We will first address the important features of both cyclization strategies, and then show how the combination of the two can provide an effective solution to the problem posed by trans-fused bis(oxepanes). 

The second strategy is to replace the vinylene bridges of PPV (B) by a heteroatom possessing a lone pair that can participate in the n-conjugation [4]. Representative examples of this class of derivative (D) (Fig. 1) are the polyanilines and poly(p-phenylenesulfide) [la,b]. 

Salvadori et al. [62] tested the same strategy but derived the bis(oxazohne) ligands in such a way that they minimized the steric hindrance at the bridging methylene carbon (structure 53 in Scheme 25). The polymer was used affording enantiomeric excesses superior to 90% and was reused at least five times with almost no loss in enantioselectivity or activity. 

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