Macro-olefination reaction

The complex structure of the macrolide bryostatin 1, 343, in addition to its activity against various forms of cancer, has made it the subject of a number synthetic studies [145]. One of the more difficult functionalities to incorporate in a stereoselective fashion into the molecule are the two trisubstituted exocyclic unsaturated esters. Evans and Car-reira addressed this problem in a novel way by using a tethered phosphonate in a macro-olefination reaction (Scheme 10-116) [146]. 

However, these same authors " realized their goal when they effected macro-cyclization via an intramolecular olefination reaction (Scheme 1.400). Again, the... 

Preparations of macro-initiators or telechelic polymers by cationic methods have been executed primarily by polymerizing isobutylene in the presence of a co-initiator that also functions as a chain transfer agent. A typical reaction sequence is shown in Scheme 1, outlining the synthesis of difunctional polyisobutylene (PIB), which is then used to initiate the polymerization of a-methyl styrene (ffi-MS) to produce an A-B-A type block copolymer. By similar methods, polyisobutylenes with phenol, phenyl, cyclopentadiene, and olefin termini have been synthesized. 

Methanol transformation to olefins over SAPO-34 catalyst is featured by high exothermicity (Alwahabi and Froment, 2004b) and rapid deactivation (Chen et al., 1999 Parket al., 2008). Considering these, circulating fluidized bed is used for MTO process in industry. The model describing reaction-diffusion process in this macro reactor is called macroscale model. However, it should be pointed out that the focus of macroscale model on reaction and diffusion is far different from microscale model. 

Alkyne RCM reactions provide not only a useful macrocyc-Uzation technique but also a solution to avoid the issue on the unpredictable alkene geometry by olefin RCM macro-cycUzations. Thus, the Lindlar reduction of the formed cyclic alkynes leads to cyclic Z-alkenes, and the methodology has been widely employed in natural product syntheses.The hydrosilylation-protodesilylation of the cyclic alkynes " is the secured access to cyclic E-alkenes. As described below, the alkyne RCM-based strategies with the subsequent transformations indicated their usefiilness in target-oriented syntheses. 

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