Abstract
The stereochemistry of the base-catalysed addition–elimination method for cyclopropane ring synthesis, employing a βγ-unsaturated phenyl sulphone and an αβ-unsaturated ester, has been examined. The olefinic geometry of the βγ-unsaturated sulphone is retained in the product, and the unsaturated side chain and the ester function emerge trans about the ring, with substantial stereoselectivity. On the other hand, the geometry of the double bond of the αβ-unsaturated ester becomes equilibrated in the anion addition product. Thus the resulting cyclopropanes are produced without a stereoselective preference based on the geometry of the original αβ-unsaturated ester. This work has led to the synthesis of ethyl 2,2-dimethyl-trans-3-[(1E,5E)-2,6,10-trimethylundeca-1,5,9-trienyl]cyclopropanecarboxylate (40) and the corresponding cyclopropylmethanol (42), representing one side of the presqualene molecule, and to the pair of C-2 epimeric diterpenoid ethyl 2-[(E)-4,8-dimethylnona-3,7-dienyl]-2-methyl-trans-3-(2-methylprop-1-enyl)cyclopropanecarboxylates (44) and (45) and the corresponding alcohols (47) and (48), representing the other side of the presqualene molecule. Lower prenylogues were also studied.By using phenyl 3,7,11-trimethyldodeca-2,6,10-trienyl sulphone (37) and ethyl (2E,6E)-3,7,11-trimethyl-dodeca-2,6,10-trienoate (39; R = Et), the stereochemically controlled synthesis was developed to give two stereoisomers of presqualene esters (49) and (50), which were separated and reduced to give (±)-natural presqualene alcohol (53) and the C-2 epimer (54); tritiated samples were also prepared. Chemical and biological comparison with natural presqualene alcohol, the C30 compound involved in squalene biosynthesis, confirmed the identification. An n.m.r. study with shift reagents was used to investigate the stereochemistry of these and related subsituted cyclopropanes.Condensation of the C20 sulphone (64) with the C20 ester (62) led, in a similar synthesis, to the C40 cyclopropane carotenoid precursor (±)-prephytoene alcohol (68) and its C-2 epimer (69).
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
