The silyl‐protected allylhydropentalenone derivative 9, derived from the Weiss diketone, was functionalized by enantioselective deprotonation in the presence of lithium bis(1‐phenylethyl)amide/LiCl as the chiral base, which was generated in situ from bis(1‐phenylethyl)ammonium chloride [(R,R)‐ or (S,S)‐14] and BuLi, and trapping of the resulting enolate with alkyl halide electrophiles to give pseudo‐C2 or ‐Cs‐symmetrical bicyclo[3.3.0]octanones 10 and 11. The influence of the chiral base and electrophiles on the regioselectivity and double stereodifferentiation was investigated. Taking the double stereocontrol into account, a matched selectivity for the pseudo‐C2 pair (1R,4R)‐10/(1S,4R)‐10 and a mismatched selectivity for the pseudo‐Cs pair (1S,6R)‐11/(1R,6R)‐11 were observed in the presence of (R,R)‐14. The use of (S,S)‐14, however, produced a mismatched selectivity for (1R,4R)‐10/(1S,4R)‐10 and a matched selectivity for (1S,6R)‐11/(1R,6R)‐11 with complementary diastereoselectivity depending on the electrophile. Furthermore, the hydropentalenone derivative 10a provided an alternative route to the bicyclo[3.3.0]octene core of the macrocyclic tetramic acid lactam, cylindramide (5).
Functionalized hydropentalenes (i.e., bicyclo[3.3.0]octanones) constitute important building blocks for natural products and for ligands for asymmetric catalysis. The assembly and tailored functionalization of this convex roof-shaped scaffold is challenging and has motivated a variety of synthetic approaches including our own contributions, which will be presented in this account.1 Introduction2 Biosynthesis of Hydropentalenes3 Hydropentalenes through the Pauson–Khand Reaction4 Hydropentalenes through Transannular Oxidative Cyclization of Cycloocta-1,4-diene5 Functionalization of Bicyclo[3.3.0]octan-1,4-dione to Dodecahydrocyclopenta[a]indenes6 Functionalization of Bicyclo[3.3.0]octan-1,4-diones to Crown Ether Hybrids7 Functionalization of Bicyclo[3.3.0]octan-1,4-dione to Cylindramide8 Tandem Ring-Opening Metathesis/Ring-Closing Metathesis/Cross-Metathesis of Bicyclo[2.2.1]heptanes9 Functionalization of Bicyclo[3.3.0]octan-1,4-dione to Geodin A10 Hydropentalenes through Enantioselective Desymmetrization of Weiss Diketones11 Functionalization of Weiss Diketones by Carbonyl Ene Reactions12 Functionalization of the Weiss Diketone to Cylindramide and Geodin A Core Units13 Biological Properties of Bicyclo[3.3.0]octanes14 Hydropentalenes through Vinylcyclopropane Cyclopentene Rearrangement15 Functionalization of Bicyclo[3.3.0]octanes toward Chiral Dienes16 Miscellaneous Syntheses of Hydropentalenes17 Conclusion and Outlook
CitationSAR studies on hydropentalene derivatives--Important core units of biologically active tetramic acid macrolactams and ptychanolides. 2014, 22 (13)
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