An enantio- and diastereoselective stepwise cyclization of polyprenoids induced by Lewis acid-assisted chiral Bronsted acids (chiral LBAs) and achiral LBAs is described. In particular, the absolute stereocontrol in the initial cyclization of polyprenoids to form an A-ring induced by chiral LBAs and the importance of the nucleophilicity of the internal terminator in polyprenoids for the relative stereocontrol in subsequent cyclization are demonstrated. (−)-Ambrox was synthesized via the enantioselective cyclization of (E,E)-homofarnesyl triethylsilyl ether with tin(IV) chloride-coordinated (R)-2-(o-fluorobenzyloxy)-2‘-hydroxy-1,1‘-binaphthyl ((R)-BINOL-o-FBn) and subsequent diastereoselective cyclization with CF3CO2H·SnCl4 as key steps. Protection of (E,E)-homofarnesol by a triethylsilyl group increased the enantioselectivity of chiral LBA-induced cyclization and both the chemical yield and diastereoselectivity in the subsequent cyclization. The enantioselective cyclization of homo(polyprenyl)arenes posses...

Enantio- and diastereoselective stepwise cyclization of polyprenoids induced by chiral and achiral LBAs. A new entry to (-)-ambrox, (+)-podocarpa-8,11,13-triene diterpenoids, and (-)-tetracyclic polyprenoid of sedimentary origin.

Syntheses of polycyclic isoprenoids have been achieved by several groups; however, no general “biomimetic” method has yet been reported In this paper we describe the biomimetic cyclization of simple isoprenoids to polycyclic isoprenoids using Lewis acid-assisted chiral Bronsted acids, “chiral LBAs” This is the first example of a proton-induced enantioselective ene cyclization in synthetic chemistry Geranyl phenyl ethers, o-geranylphenols, and geranylacetone derivatives were directly cyclized at −78 °C in the presence of (R)-binaphthol derivatives and tin tetrachloride During the cyclization, [1,3] abnormal Claisen rearrangement often took place The enantioselectivities were up to 90% ee Compounds bearing a farnesyl group could also be cyclized under the same conditions to give the natural products (−)-Ambrox and (−)-chromazonarol These chiral LBAs recognize a trisubstituted terminal olefin enantiotopically and generate site-selective carbocations on the substrates The absolute stereochemistry of t

Enantioselective Biomimetic Cyclization of Isoprenoids Using Lewis Acid-Assisted Chiral Brønsted Acids: Abnormal Claisen Rearrangements and Successive Cyclizations

Synthesis of Ambrox® from (−)-sclareol and (+)-cis-abienol

15 – The Fragrance of Ambergris

On a prepare par degradation du sclareol, le bicyclohomofarnesal, le bicyclohomofarnesol, et la tetramethyl-1,1,6,10-ethyl-5-oxido-6,52-decaline.

Odeur et Constitution III. Les substances bicyclohomofarnésiques

La reduction de la lactone I, de l'hydroxyacide VI, de l'acetoxyacide VII ou de l'ozonide de l'oxyde non sature XII par l'hydrure de lithium-aluminium donne le glycol II avec un bon rendement.

M. Hinder

Papers

Odeur et constitution IV. Sur les époxydes hydroaromatiques à odeur ambrée