Cyclizations 2- trimethylsilyloxy-1,3-butadiene

The hetero-Diels-Alder cyclization reaction of tra s-l-methoxy-3-trimethylsilyloxy-1,3-butadiene (Si) (= Danishefsky s diene) with benzaldehyde (S ) (Scheme 12.23) [217-221] is a promising reaction for evaluating the catalytic properties of Lewis acidic lanthanide centers, and has enormous potential for asymmetric synthesis of natural products (e.g., monosaccharides) [222-225]. 

Ln = Sc, Y, La), and have been tested as heterogeneous catalyst in the Diels-Alder cyclization of terH-methoxy-3-trimethylsilyloxy-l,3-butadiene with benzaldehyde (Danishefsky transformation of 1,3-dienes), and proved active [51]. The surface yttrium bis-dionate has also been synthesized directly from the molecular precursor [Y( Bu-COCHCO-"C3F7)3] by reaction with MCM-41 surface silanols [51]. 

In a synthesis of the tricychc skeleton of FR901483 (45), Bonjoch and Sole reported a TMG (3) promoted conjugate addition reaction of nitroalkane to methyl acrylate. Reaction of methyl acrylate (40) and nitro acetal 41 [9,10], obtained from Diels-Alder reaction between nitroethylene and 2-(trimethylsilyloxy)-l,3-butadiene, gave nitro ester 42 in 71% yield. The ester 42 was further converted to the spiro compound 43, and a palladium promoted cyclization reaction led to the azatricyclic skeleton 44 (Scheme 7.7). 

The latter reacting with P2O5 gave rise to fluoroalkylthio(trifluoroacetyl)ketenes 13, which were demonstrated to act as heterodienes in the Diels-Alder reaction with phenylacetylene to form 4-pyrones 14 [ 11], Langer et al. reported that the McsSiOTf-mediated cyclization of l,3-bis(trimethylsilyloxy)-l,3-butadienes 15 with4,4-dime-thoxy-l,l,l-trifluorobut-3-en-2-one resulted in the formation of trifluoromethylated pyran-4-ones 16 [12] (Scheme 7). 

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See also in sourсe #XX -- [ ]

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