β-Alkoxycarbonyl Enol Triflates as Precursors of Stereopure 3-Ene-1,5-diyne Building Blocks for the Chromophores of Neocarzinostatin, C-1027, Kedarcidin, Maduropeptin, and N1999A2

Olaf Gebauer; Reinhard Brückner

doi:10.1055/s-2000-6366

Synthesis 2000; 2000(4): 588-602
DOI: 10.1055/s-2000-6366

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β-Alkoxycarbonyl Enol Triflates as Precursors of Stereopure 3-Ene-1,5-diyne Building Blocks for the Chromophores of Neocarzinostatin, C-1027, Kedarcidin, Maduropeptin, and N1999A2

Olaf Gebauer^* , Reinhard Brückner

^*Geschäftsbereich Pflanzenschutz, BAYER-AG, PF-F-S1 Fungizide, Alfred-Nobel-Str. 50, 40789 Monheim, Germany; Fax +49 (21 73) 38 39 26; E-mail: olaf.gebauer.og@bayer-ag.de

Abstract

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A 5-step synthesis of α-alkoxymethyl-, α-siloxymethyl- and α-(carbamoyloxy)methyl-substituted enediynes 7 from type 23 β-oxo esters was developed following the strategy of Scheme 2. Specifically, the β-oxo esters 33, 36 and 38 (prepared as shown in Scheme 4) and NaH (or t-BuLi) gave Z-enolates in THF and E-enolates in DMF which were scavenged as enol triflates Z-27a-c and E-27a-c, respectively, upon treatment with triflimides 40 or 41 (Scheme 5). The Z-configurated enol triflates underwent Cacchi couplings with (trimethylsilyl)acetylene to give the pent-2-en-4-yne-1-carboxylates E-42a-c (Scheme 5). These were reduced to the corresponding aldehydes E-44a-c (Scheme 6) which were homologated with lithio(trimethylsilyl)diazomethane to furnish the desired enediynes 45a-c as pure E-isomers.

C-C couplings - enediynes - enynes - β-oxo esters - stereoselective enolate formation

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