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26.9.1.1.10 Method 10: Cyclocondensation of Danishefsky-Type Dienes with Alkenes

DOI: 10.1055/sos-SD-026-00987

Marsden, S. P.Science of Synthesis, (2005261086.

1-Alkoxy-3-siloxybutadienes are extremely reactive dienes for DielsAlder cycloaddition reactions. The parent compound, 1-methoxy-3-trimethylsiloxybuta-1,3-diene (230), has become known as Danishefsky's diene, and this name is also commonly applied to the general class of reagents. The initially formed cycloadducts from 230 and dienophiles such as methyl acrylate and 2-methylpropenal are β-alkoxy silyl enol ethers, and these can readily be converted into the corresponding cyclohexenones such as 231 via hydrolysis to the ketone and β-elimination (Scheme 42).[‌190‌,‌191‌] The method gains further power when applied to cycloadditions with endocyclic dienophiles, leading to fused ring systems.[‌191‌‌193‌] The diene is sufficiently reactive to take part in cycloadditions even with poorly reactive dienophiles such as 2-methylcyclohex-2-enone (3), giving Decalin derivative 232.[‌191‌] The reaction has similarly been applied to the synthesis of bicyclic amines for alkaloid synthesis (e.g., 234) utilizing nitrogen-containing dienophiles such as 233.[‌193‌] The reaction can be accelerated by the application of microwave irradiation,[‌194‌] high pressure, or by use of Lewis acids.[‌195‌]

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