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Structure-Odor Correlation, VII. - Synthesis and Olfactive Properties of Theaspirane Analogues
Weyerstahl, Peter,Buchmann, Bernd,Marschall-Weyerstahl, Helga
, p. 507 - 524 (2007/10/02)
The spirodihydrofurans 8-12 were prepared by addition of the respective alkynols to the ketone 20 (-->21-25), Lindlar hydrogenation (-->26-30), and cyclization. - The saturated derivatives 1-6 were available either by hydrogenation (8-10-->1,2,4) or via the lactol 47 and its reaction to the diols 31-36.Addition of the ethyl acetate anion to 20 (-->71), reduction (71-->73), and cyclization yielded the spirooxetane 13. - From the ynediols 76 and 77, Lindlar hydrogenation (-->78,79), cyclization (-->80,81), and further hydrogenation led to the spirotetrahydropyranes 16and 17. - Key compound for the synthesis of the ketone 18 was the geranic acid derivative 94, which could be obtained in two different ways.Cyclization of 94 to the diester 92 and Dieckmann condensation of 92 under simultaneous methylation (-->99) led to 18.The diastereoisomers 18a and b could be assigned after reduction of 18 to the separable alcohols 19a-c. - The olfactive properties (strength and quality) of the theaspirane analogues are determined by the conformational flexibility of the respective molecule.Thus, the almost rigid 13 has a very strong camphoraceous-herbaceous odor.Augmenting flexibility, particularly by increasing of the ring size (-->1,-->16), but also by alkyl substitution at C-2, results in remarkably weaker, woody-flowery notes.
