Synthesis of γ‐Lactones from Cycloocta‐1,5‐diene − Starting Materials for Natural‐Product Synthesis

The bislactones rac ‐tetrahydro‐2,2′‐bifuranyl‐5,5′‐dione ( rac ‐ 12 ) and its diastereomer meso ‐ 25 were prepared from endo ‐5‐hydroxy‐9‐oxabicyclo[4.2.1]nonan‐2‐one ( endo ‐ 10 ) and endo ‐6‐hydroxy‐9‐oxabicyclo[3.3.1]nonan‐2‐one ( endo ‐ 11 ) or exo ‐5‐hydroxy‐9‐oxabicyclo[4.2.1]nonan‐2‐one ( exo ‐ 23 ), respectively, under the conditions of a Baeyer−Villiger oxidation with trifluoroperacetic acid. The latter compounds were obtained by O ‐heterocylization of cis , cis ‐cycloocta‐1,5‐diene ( 1 ) by either reaction with peracids followed by hydrolysis and Jones oxidation or ruthenium tetraoxide oxidation, respectively. The optically active bislactone ( R , R )‐(−)‐ 12 was prepared in a similar manner from (1 S ,5 R ,6 R )‐(+)‐ 10 and (1 R ,5 R ,6 R )‐(+)‐ 11 , which, in turn, were obtained by lipase‐catalyzed asymmetric acetylation of the corresponding diols meso ‐ 2 and rac ‐ 3 and subsequent Jones oxidation of the formed hydroxy esters (1 S ,2 S ,5 R ,6 R )‐(+)‐ 4 and (1 R, 2 R ,5 R ,6 R )‐(+)‐ 5 . Since the regioisomeric hydroxy‐9‐oxabicyclo[4.2.1]‐ and ‐[3.3.1]nonan‐2‐ones (1 S ,5 R ,6 R )‐(+)‐ 10 and (1 R ,5 R ,6 R )‐(+)‐ 11 yielded the same bislactone [( R , R )‐(−)‐ 12 ] it is presumed that the sequence proceeds via open‐chain intermediates. Applying this strategy to the enantiopure acetoxy ketones (1 S ,5 R ,6 R )‐(+)‐ 8 and (1 R ,5 R ,6 R )‐(+)‐ 9 , followed by Kolbe electrolysis of the formed ( R , R )‐5‐acetoxy‐7‐carboxyheptan‐4‐olide [( R , R )‐ 27 ], ( R , R )‐5‐acetoxydecan‐4‐olide [( R , R )‐ 29 ] was accessible in a five‐step synthesis. The absolute configuration of (+)‐ 8 was determined by X‐ray analysis of the dithiepane derivative 14 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)