Synthese der enantiomeren 1,6‐Spiro[4.4]nonadiene

Two new syntheses of spiro[4.4]nonane‐1, 6‐dione (I) are described: one by rearrangement of 1,6‐epoxy‐bicyclo[4.3.0]‐nonane‐2‐one (IV) with boron trifluoride, the other by an acid catalyzed, intramolecular Claisen condensation of 4‐(2‐oxocyclopentyl)‐butyric acid. Spiro[4.4]‐nonane‐1,6‐dione is converted into trans, trans‐spiro[4.4]nonane‐1,6‐diol which is resolved into enantiomers via the diastereomeric esters with (−)‐camphanic acid. (+)‐(5S)‐Spiro[4.4]nona‐1,6‐diene (III) is prepared from (1R, 6R)‐trans,trans‐spiro[4.4]nonane‐1,6‐diol (II) by pyrolysis of the corresponding bis‐4‐methylphenyl‐thionocarbonate. This modification of the Chugaev reaction is particularly useful with sterically hindered alcohols which cannot be converted into S‐me‐thylxanthates. The circular dichroism, UV.‐ and NMR.‐spectrum of optically active spiro[4.4]‐nonane‐1,6‐diene are discussed.