Tethered approach connection

Alexander approach to spherical geometries, while making the connection between tethered chains and branched polymers. The internal structure of tethered layers was illuminated by numerical and analytical self-consistent field calculations, and by computer simulations. 

Zwitterionic structures with a borate anion covalently attached to a cyclopentadienyl donor can be obtained by a number of synthetic approaches. In the known compounds, the means by which the borate is tethered to the ring has a significant impact on the properties of the zwitterions. In particular, the length of the tether connecting the ring with the borate is crucial for the stability and intramolecular ion-ion contacts. For example tris cyclopentadienyl zirconium betaine complex in which boron atom is directly bonded to Cp can be generated from boron substituted cyclopentadienyl anion (equation 21). ... 

Another conceptually different approach to discriminating the nucleophilic attack at two allyl terminus of symmetrical r) -allyl intermediate was used earlier than those described above [119], As shown in Scheme 8.64, a functional group capable of interacting with nucleophile was connected by a long tether to the one side of chiral diphosphines in order to bring the nucleophile close to only one allyl terminus. For example, chiral ferroceny diphosphines shown in Scheme 8.64 provided fairly high enantioselectivity in allylic alkylation. 

Further improvements in modeling flexible sheet polymers must take into account the molecular connectivity within the membrane. To analyze the shapes of these structures, one discards elasticity theory and finds a more appropriate context in statistical mechanics of random surfaces. A number of approaches have been proposed. For example, the membrane may be (a) represented as a self-avoiding surface,"i2.i99 and its shape characterized by asphericity and radius of gyration,"i2.i99 or (b) viewed as a tethered surface with fixed internal connectivity.200-203 in case (b), nuclei are regarded as hard spheres tethered together by elastic or fluid strings, forming a net with a specified architecture. 

More unusual IMDAF reactions involve 2-vinylfuran as an extra-annular diene in which vinyl and furan C4-C5 double bond act as a diene. This synthetic approach was employed by Harwood in the synthesis toward colletofraga-rone A1 (Scheme 18) [31]. The intramolecular reaction showed that the use of a 2-vinylfuran substrate 73 with the dienophile connected by a tether chain at C-4 of the furan nucleus, formed a single tricyclic adduct 74 with a similar skeleton to that of the tricyclic core of colletofragarones. In this instance, the mildness of the high-pressure conditions permits the cycloadducts to be isolated without subsequent isomerization of the double bond to reform the furan, and in greatly superior yields to the thermal conditions (benzene 80 °C, 24 h, 28%). 

---