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 labdanolic acid

The synthesis of (-)-ambrox starting from labdanolic acid

The synthesis of Ambrox -like compounds starting from (+)-larixol. Part 2

Ambrox®: Unwiderstehliche Duftnote

The development of a new synthetic approach to (−)-Ambrox® (37) and epi-Ambrox® (29) using thujone (1) as a chiral synthon, is presented. Thujone (1), a readily available starting material obtained from Western red cedar, can be efficiently converted to β-cyperone (2) and the latter is then chemically elaborated to the key intermediate, the enone 6. A carbonyl transposition of 6 to enone 9 also allows a formal synthesis of (−)-Polywood® (18). Keywords: thujone, β-cyperone, (−)-Ambrox®, epi-Ambrox®, synthesis.

Carles Cirera

Papers

The chemistry of thujone. XX. New enantioselective syntheses of Ambrox and epi-Ambrox