Synthesis of the spirosesquiterpene (−)-acorenone and related cyclopentanoid monoterpenes

Abstract

The first total synthesis of the spirosesquiterpene (−)-acorenone (1) is described. The critical step involves a spiroannelation of the enamine of aldehyde 11 with 1-methoxy-3-buten-2-one (16) in the presence of acetic acid to give ketone 17. Reaction of 17 with methylmagnesium iodide followed by treatment of the resultant alcohol 18 with p-toluenesulfonic acid in refluxing benzene leads directly to 1 in good overall yield. As the starting material for the preparation of the cyclopentanoid aldehyde 11 was (+)-limonene the final product is optically active and thus the absolute configuration of naturally occurring (−)-acorenone (1) is established. The preparation of a number of other optically active cyclopentanoid monoterpenes (4 and 13) is also described.

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part I: Dihydronepetalactones

“…Due to the CH-acidity at the α-position of the formyl group, epimerization of the all- trans product 24 under acidic or basic conditions could be expected. Lange et al reported the catalytic hydrogenation of a structurally close analogue, (5 R )-1-formyl-2-methyl-5-isopropylcyclopent-1-ene, over Pd/C (10%) to give a 9:1 mixture of the all- cis versus the all- trans product [ 29 ]. In our case, the application of Lange’s method to the aldehyde 23 led to the formation of a 3:1 mixture of the all- cis versus the all- trans epimer.…”

Stereoselective Intermolecular [2 + 2]-Photocycloaddition Reactions and Their Application in Synthesis

“…Plenty of examples have been reported in the literature. [79][80][81][82][83][84][85][86][87] The approach from the less shielded face is favored and there are no significant exceptions to this rule. In this regard the stereochemical outcome of photocycloadditions to chiral alkenes is more readily predictable than the one of photocycloadditions of chiral alkenones.…”

Cover Picture: Peptide Electron Transfer: More Questions than Answers (Chem. Eur. J. 18/2005)

“…The reported optical rotation for natural 3a from T. koningii is [ α ] D 26 = –5.2 ( c = 0.12, CHCl 3 ),8 and the specific rotation of the synthetic material ent ‐ 3a is [ α ] D 17 = +5.5 ( c = 0.12, CHCl 3 ), confirming that both species produce the same enantiomer of 3a . Furthermore, the specific rotation of synthetic ent ‐ 4 ,[ α ] D 17 = +44.0 ( c = 0.02, CHCl 3 ), exhibited the opposite sign as reported for the oxidation product 4 obtained from natural 3a from T. koningii , [ α ] D 26 = –22.0 ( c = 0.047, CHCl 3 ), and for natural 4 isolated from Acorus calamus , [ α ] D 25 = –28 (CCl 4 ) 8,13c…”