Additions 1 -methoxy-2-methyl-1 - propene

Preparation 3-4 A 12 / flask was equipped with a mechanical stirrer, thermometer, N2 inlet, drying tube outlet, and addition funnels. Tetrahy-drofuran and p-xylene were charged to the flask. The catalyst tetrabutyl ammonium m-chlorobenzoate, as solution in acetonitrile, was then added. Then the initiator, l-methoxy-l-trimethylsiloxy-2-methyl propene was injected. 2-Dimethylaminoethyl methacrylate was added during 45 min. Then, butyl methacrylate, was added during 30 min. Some time afterwards dry methanol was added to the solution and distillation started to remove the solvent. After completion of the distillation, isopropanol was added. 

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. 

Intermolecular addition of carbon nucleophiles to the ri2-pyrrolium complexes has shown limited success because of the decreased reactivity of the iminium moiety coupled with the acidity (pKa 18-20) of the ammine ligands on the osmium, the latter of which prohibits the use of robust nucleophiles. Addition of cyanide ion to the l-methyl-2//-pyr-rolium complex 32 occurs to give the 2-cyano-substituted 3-pyrroline complex 75 as one diastereomer (Figure 15). In contrast, the 1-methyl-3//-pyrrolium species 28, which possesses an acidic C-3-proton in an anti orientation, results in a significant (-30%) amount of deprotonation in addition to the 2-pyrroline complex 78 under the same reaction conditions. Uncharacteristically, 78 is isolated as a 3 2 ratio of isomers, presumably via epimerization at C-2.17 Other potential nucleophiles such as the conjugate base of malononitrile, potassium acetoacetate, and the silyl ketene acetal 2-methoxy-l-methyl-2-(trimethylsiloxy)-l-propene either do not react or result in deprotonation under ambient conditions. 

This reaction of silyl ketene acetals with aldehydes, using 29 as a stoichiometric chiral reagent (Eq. 46), was reported by Reetz et al. [42]. The aldol addition of l-(trimethyl-siloxy)-l-methoxy-2-methyl-l-propene and 3-methylbutanal provides the aldol in only 57 % yield, but with 90 % ee. 

Scheme 55. Tandem electrophile/nucleophile addition to the y -benzene ligand of TpRe(CO) (MeIm)(f/ -benzene) (MMTP = l-methoxy-2-methyl-l-(trimethylsiloxy)propene).

Scheme 56. 1,2-Tandem addition of H /l-methoxy-2-methyl-l-(trimethylsiloxy)-propene (MMTP) to...

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