Enantioselective synthesis of spiro[4.4]non- and spiro[4.5]dec-2-ene-1,6-diones

Facile Synthesis of Spirocyclic Systems through the Intramolecular Addition of Ketyl Radicals via the Sodium/Ammonia Reduction of δ,ε-Unsaturated Carboxylic Esters

“…The reaction is general when an olefinic bond is present but is somewhat sensitive to steric hindrance. Furthermore, because unsaturated β-hydroxy esters can be synthesized with good enantioselectivity, the spirocyclic compounds could be obtained with good enantioselectivity.…”

A Facile Synthesis of (n+3) and (n+4) Ring-Enlarged Lactones as well as of Spiroketolactones from n-Membered Cycloalkanones

“…4c Instead of first preparing g-hydroxy ketones 5 and relying on their often unfavorable equilibration to hemiketals 2, we now used a direct approach to the latter starting from ethyl 1-allyl-2-oxocycloalkanecarboxylates 1, readily accessible by allylation of ethyl 2-oxocycloalkanecarboxylates. [8][9][10][11][12][13] Indeed, initial studies on the iodination of the allylated cyclohexanone 1b in wet chloroform at room temperature or…”

A Practical Asymmetric Synthesis of Enantiopure Spiro[4,4]nonane‐1,6‐dione

“…The combined organic phase was dried over anhydrous sodium sulfate and then filtered. After removal of the solvent by vacum evaporation, the residue was submitted to column chromtography separation on silica gel using petroleum ether/EtOAc (20:1-10:1) as eluent to afford (R)-14 as a pale yellow oil; yield: 12 …”

“…[6][7][8][9][10][11][12] The resolution of racemic 1 was realized in 1977 by repeated recrystallization of the hydrazone diastereomers of (S)-2-oxo-2-(1-phenylethylamino)acetohydrazide, followed by removal of the hydrazone in refluxing acetone/water. Enantiopure BINOL was also found to be able to separate two enantiomers of racemic 1 through enantioselective molecular complexation, affording optically pure BINOL·1 in up to 19% yield after recrys-tallization.…”

“…Stoichiometric amounts of optically pure 1,2-diols have been used to form a chiral ketal auxiliary for asymmetric induction in the allylation of 2-oxocyclopentanecarboxylate ester with allyl bromide to generate a quaternary carbon center. [12] As described above, although a variety of methodologies for the synthesis of optically active 1 has been reported, [6][7][8][9][10][11][12][13] the accessibility of both (R)-1 and (S)-1 with > 99% ee values still remains a challenging issue in terms of practicality. In the present work, we report a concise asymmetric synthesis of enantiopure (R)-1 and (S)-1 from readily available starting material with facile manipulations.…”