Terpenes in organic synthesis

A seven-step synthesis ofS-(+)-hydroprene (S-1) in 20 % overall yield starting fromS-(+)-3,7-dimethyl-1,6-octadiene (2) of 55+-10 % optical purity is described. The introduction of an optical enhancement step in the synthetic sequence at the stage ofS-(–)-3,7-dimethyl-1-octanol (9) raises the optical purity ofS-1 from 50 % to 80 %.For part 13, see. ref.¹ Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 342–348, February, 1993.     

Attractant pheromones of coleoptera. Communication 1. Simple synthesis of exo- and endo-brevicomins using the oxy-cope rearrangement

Conclusions A five-stage synthesis of exo- and endo-brevicomins was carried out from acrolein and methyl vinyl ketone, with an oxy-Cope rearrangement of 4-ethyl-3-methyl-1,5-hexadien-3-ol as the key stage.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1887–1890, August, 1985.     

Lipase-mediated deracemization of secondary 1-phenyl-substituted propargylic alcohols of different topology

Acetylation of (±)-1-phenylnon-2-yn-1-ol, (±)-1-phenylhept-1-yn-3-ol, and (±)-1-phenylundec-4-yn-3-ol ((±)-5) in the presence of lipase from Candida cylindracea (CCL) proceeds slowly to give products with ee 20%. The acetates of these alcohols are hydrolyzed in the presence of porcine pancreatic lipase (PPL) equally unsatisfactorily. The (⁶-arene)tricarbonylchromium complex of alcohol (±)-5 is acetylated in the presence of CCL up to 22% conversion to give (R)-acetate whose oxidative decomplexation followed by saponification results in alcohol (R)-(–)-5 with ee 95%. The configuration of alcohols (–)-5 and (+)-5 was determined by NMR spectroscopy of their esters with (R)- and (S)-Mosher"s acids.     

Terpenes in organic synthesis

All four stereoisomers of 2,6-diniethyloctan-1-ol, the nearest precursors of the title formates, were synthesized in five to eight stages, with configurational purity ranging from 41 to 96 %, employing a stereodivergent scheme based on the partial hydrolysis of two pseudoracernic substrates, (2RS,6R)-2,6-dimethyloct-1-yl formate and (2RS,6S)-2,6-di-methyloct-1-yl acetate, in the presence of porcine pancreatic lipase (PPL). Configurations and diastereomeric compositions of the alcohols thus obtained were determined by correlating the latter with (S,S)-4,8-diniethyldecanal, prepared on the basis of enantioselective biohydrogenation of (R)-2,6-dimetliylocta-2,7-dienal with bakers' yeast, and by comparing the [α]_D values of the alcohols with their NMR data and/or with those of their (S)-MTPA derivatives. The attractant potency of stereoisomeric 2,6-diniethyloct-1-yl formates towardsTribolium confusum was found to vary depending on their diastereomeric composition. The configuration at C(6) exerts some influence on the stereoselectivity of the PPL-catalyzed hydrolysis of pseudoracemic 2,6-dimethyloct-1-yl formates.[/p]     

Pheromones of coleoptera Communication 4. Synthesis of multistriatin with the application of the thermal hydroxy-cope rearrangement under high pressure

Conclusion The synthesis of multistriatin (in the form of the , , and isomers) was accomplished in three stages from 2-methyl-1-penten-3-one (IV) with the total yield of 13%. The thermal hydroxy-Cope rearrangement of 3-ethyl-2-methyl-1,5-heptadien-3-ol (II) at the pressure of 10 kbar was utilized at the key stage of the synthesis.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2776–2780, December, 1986.     

Enantioselectivity of enzymatic acylation of some structurally various racemic alcohols in anhydrous aprotic media

Partial acylation of (R,S)-3,7-dimethyloctan-1-ol (1) and (R,S)-7-methoxy-3,7-dimethyloctan-1-ol (2) with vinyl acetate catalyzed by the lipase fromCandida cylindracea affords in good yields the correspondingS-configured acetates with 92–98% enantiomeric excess (ee). Under similar conditions, racemic α-cyclogeraniol (3), drim-7-en-11-ol, methyl 4-(3-hydroxy-2-methylpropyl)benzoate, and its η⁶-chromium(tricarbonyl) complex (6) are acylated with rather poor (and, for the two latter, opposite) enantioselectivity, whereas (R,S)-2,4∶3,5-di-O-benzylidenexylitol remains unaffected. Racemic isoborneol (8) and 2-nitro-1-phenylethanol also remain almost or completely unconverted. Attempts to perform enantioselective acylation of alcohols 3 and 8 with Ac₂O in the presence of porcine pancreatic lipase (PPL) proved equally unsuccessful. By contrast, the PPL-catalyzed acylation of alcohol 6 with vinyl acetate at 17% conversion affords the levorotatory acetate (S)-6a withca. 100%ee. PPL-Mediated partial acylation of (R,S)-pantolactone with Ac₂O, followed by mild deacylation of the resultingR acetate, gives (R)-(-)-pantolactone of 97% enantiomeric purity in 60% overall yield. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 175–186, January, 1997.     

New ways to determine the absolute configurations of alkyl 6-R-cyclohexa-1,3-dienecarboxylates

Two new methods for the determinatuion of the absolute configuration of methyl 4-methyl-6-(2-methylprop-1-enyl)cyclohexa-1,3-dienecarboxylate are proposed, and the configurations attributed previously to its (+)- and (–)-enantiometers are confirmed. Chiral methyl carboxylate is converted into the corresponding alcohol whose configuration is deduced from either the rate of hydrolysis of the respective racemic acetate in the presence of pancreatic lipase (method 1) or from the difference between the Eu(fod)₃-induced shifts of the MeO signals in the ¹H NMR spectra of the diastereomeric esters of S- or R-Mosher"s acid (method 2).