178231-89-5Relevant academic research and scientific papers
Stereoselective synthesis of freelingyne and related γ-alkylidenebutenolides via vinylogous Mukaiyama aldol additions
Von der Ohe,Bruckner
, p. 659 - 669 (2000)
Following the strategy of Scheme 1, a Mukaiyama aldol addition/anti-elimination route to stereopure γ-alkylidenebutenolides 4 was established. The addition giving 27 was only moderately diastereoselective but the products lk- and ul-27 were chromatographically separable (Scheme 4). They underwent highly selective anti-eliminations in the presence of triflic anhydride-pyridine or Burgess' reagent, furnishing the thiophene-containing butenolides Z- and E-28, respectively (Scheme 5). The Mukaiyama aldol addition leading to compound 29 was 100% lk-selective when mediated by BF3 etherate and 87 : 13 ul-selective in the presence of ZnBr2 (Scheme 6). Stephens-Castro couplings of the resulting butenolides lk- and ul-29 with 3-ethynylfuran proceeded with complete conservation of the stereochemical integrity (Scheme 7). The subsequent anti-eliminations of water were best realized by treatment with DEAD-PPh3. They provided freelingyne (Z-9) with ds = 92 : 8 and its isomer E-9 with ds = 98 : 2 (Scheme 8). Analogously, the differently substituted (trimethylsiloxy)furans 15 or 16 provided the freelingyne analogs Z-10, E-10 and Z-11 (Schemes 6-8).
