Styrene-diphenylethylene synthesis

Gausepohl et ah [31] investigated the behavior of blends between sPS and random styrene-l,l-diphenylethylene copolymers obtained by anionic synthesis. The blends were miscible for copolymer contents of 1,1-diphenylethylene lower than 15 wt% as indicated by the occurrence of a single Tg (114°C). Tm and crystallization rate were not influenced. 

The copper-catalyzed cyclopropanation of alkenes with diazoalkanes is a particularly important synthetic reaction (277). The reaction of styrene and ethyl diazoacetate catalyzed by bis[/V-(7 )- or (5)-a-phenyl-ethylsalicylaldiminato]Cu(II), reported in 1966, gives the cyclopropane adducts in less than 10% ee and was the first example of transition metal-catalyzed enantioselective reaction of prochiral compounds in homogeneous phase (Scheme 90) (272). Later systematic screening of the chiral Schiff base-Cu catalysts resulted in the innovative synthesis of a series of important cyclopropane derivatives such as chrysanthemic acid, which was produced in greater than 90% ee (Scheme 90) (273). The catalyst precursor has a dimeric Cu(II) structure, but the actual catalyst is in the Cu(I) oxidation state (274). (S)-2,2-Dimethylcyclopropanecar-boxylic acid thus formed is now used for commercial synthesis of ci-lastatin, an excellent inhibitor of dehydropeptidase-I that increases the in vivo stability of the caibapenem antibiotic imipenem (Sumitomo Chemical Co. and Merck Sharp Dohme Co.). Attempted enantioselective cyclopropanation using 1,1-diphenylethylene and ethyl diazoacetate has met with limited success (211b). A related Schiff base ligand achieved the best result, 66% optical yield, in the reaction of 1,1-diphenylethylene and ethyl diazoacetate (275). 

The synthesis of the poly[styrene-6-(hydroxystyrene-g-ethylene oxide)-6-styrene] (25), P[S-6-(HS-g-EO)-6-PS], has been reported. The backbone was a triblock copolymer, poly(styrene-6-t-butoxystyrene-6-styrene) (8), prepared by anionic polymerization by sequential addition of monomers. The protected t-butyl group was removed by treatment with HBr leading to the formation of P(S-6-HS-b-S) triblocks (9) (eq. 11). The metallation of the hydroxyl groups was performed in THF using either cumyl potassium or diphenylethylene potassium (eq. 12). The addition of EO generated the block graft copolymers (eq. 13). 

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