Methoxymethyl Methyl ether formation

Recently, Aumann et al. reported that rhodium catalysts enhance the reactivity of 3-dialkylamino-substituted Fischer carbene complexes 72 to undergo insertion with enynes 73 and subsequent formation of 4-alkenyl-substituted 5-dialkylamino-2-ethoxycyclopentadienes 75 via the transmetallated carbene intermediate 74 (Scheme 15, Table 2) [73]. It is not obvious whether this transformation is also applicable to complexes of type 72 with substituents other than phenyl in the 3-position. One alkyne 73, with a methoxymethyl group instead of the alkenyl or phenyl, i.e., propargyl methyl ether, was also successfully applied [73]. 

The formation of the methoxymethyl ether (MOM) is achieved by conventional techniques (chloromcthyl methyl ether/Afi.V-diisopropylethylamine) analogously, the methyl ether is obtained by reaction with NaH/ iodomethanc35. The, V-benzyl group is finally removed with Pd-C H,. Thus. (25.55)-2.5-bis-(inethoxymethoxymethyl)pyrrolidine is obtained yield 3.1 g (66%). 

The methoxymethyl ethers 20b could be formed by a follow-up oxidation of the methyl ethers 20a". That the less reactive but obviously more easily accessible methyl group is hereby oxidized, and not the methine hydrogen, could be a further indication of the formation of stacked associates. 

Selective formation of the methyl enol ether and reduction of the C(11) keto function followed by protection of the resultant alcohol as methoxymethyl ether provided (275). 

Like organosilyl cations stabilized by two 2-(methoxymethyl)phenyl ligands [4], 11 reacts with pyridine with transfer of a methyl group and formation of a cyclic silyl ether 17. In contrast to organosilyl cations chelated by two 2-(methylthiomethyl)phenyl ligands, a displacement of the intramolecular donors by pyridine is not possible in 12 (Scheme 3). 

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