Methoxy-2- methyl- l- trimethylsilyloxy propene

Under catalysis by tris(dimethylaminosulfonium)difluorotrimethylsilicate, 1,5-anhydro-4,6-0-benzylidene-2-deoxy-D-ery//iro-hex-3-ulo-l-enitol reacted with the ketene acetal, l-methoxy-2-methyl-l-(trimethylsilyloxy)-propene, by Michael reaction at C-1 and gave 23. When the catalyst involved was trimethylsilyl triflate the branched derivatives 24 and 25 unexpectedly resulted. These latter products were thought to arise by a trimethylsilyl triflate induced non-selective cleavage of the benzylidene acetal of the initially formed intermediate 23 affording 4-0- and 6-0-benzylic carbenium ions which underwent a subsequent ring closure at C-2. (See Chapter 13 for reaction of the same ketene acetal with glycals). ... 

Chelation control, as indicated in 5, is also a suitable model for rationalizing the stereochemical outcome of titanium tetrachloride mediated additions of 3,3-dimelhyl-2-trimethylsilyl-oxy-l-butenc (6) or l-methoxy-2-methyl-l-trimethylsilyloxy-l-propene (7) to 3-benzyloxy-2-methylpropanal (4). In both cases, there is almost exclusive formation of the chelate-controlled product (95 5 and >97 3, respectively)13. 

Related Reagents. t-Butyl a-Lithioisohutyrate Dilithio-acetate Ethyl Lithioacetate Ketene Bis(trunethylsilyl) Acetal Ketene f-Butyldimethylsilyl Methyl Acetal l-Methoxy-l-(tri-methylsilyloxy)propene l-Methoxy-2-trunethylsilyl-l-(tri-methylsilyloxy)ethylene Tris(trimethylsilyloxy)ethylene. 

When living poly(methyl methacrylate) (PMMA) prepared by group transfer polymerization (GTP) is used as a macroinitiator for the ROP of cyclic carbonates, a site transformation from the silyl ketene acetal (GTP-mechanism) to an alcoholate (anionic ROP-mechanism) with a metal-free counterion occurs (Scheme 12.5). The GTP of PMMA was initiated with l-methoxy-l-trimethylsilyloxy-2-methyl-l-propene (MTS) in combination with catalytic amounts of tetrabutyl ammonium cyanide in THF as solvent. Towards the end of the reaction, DTC is dissolved in the reaction mixture and lequiv. of fluoride anions (e.g. tris(dimethylamino) sulfonium difluorotrimethylsilicate TASF), with respect to the active species, is added. In this way, good yields of the respective block copolymers were obtained. A model experiment for this site transformation is the polymerization of DTC with MTS as the initiator and TASF as the desilylating agent. The fluoride anion promotes desilylation of the silyl ketene acetal with formation of an enolate, which reacts as a carbon-centered nucleophile with the carbonyl carbon of DTC, thereby... 

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