Synthesis of the enantiomers of lasiol, an acyclic monoterpene alcohol in the mandibular gland secretion of the male ants, Lasius meridionalis.
(2S,3S)-(-)-Lasiol (2,3,6-trimethyl-5-hepten-1-ol, 1) and its antipode were synthesized from cis-4,5-dimethylcyclohexene oxide (3) by employing asymmetric cleavage of the epoxy ring with a chiral lithium amide derived from 4 to give optically active cis-4,5-dimethyl-2-cyclohexen-1-ol (5) as the key-step.
A novel mixed dimer of a norephedrine-derived chiral lithium amide and 2-lithium-1-methylimidazole, and catalytic enantioselective deprotonation of cyclohexene oxide.
Improved stereoselectivity has been obtained by using 2-lithium-1-methylimidazole, 2, as a replacement for lithium diisopropylamide (LDA) as a bulk base in catalytic deprotonations. The chiral lithium amide 6 of (1R,2S)-N-methyl-1-phenyl-2-pyrrolidinylpropanamine, 5, has been found to deprotonate cyclohexene oxide 3 in the presence of compound 2 to yield (S)-cyclohex-2-en-1-ol, 4, in 96% ee. Compound 2 is a carbenoid species conveniently generated from nBuLi and 1-methylimidazole, 1. The base 2 has also been found to play a more intimate role in the deprotonation. Investigations by 1H, 6Li and 13C NMR of the 6Li/15N isotopologue 8 of 6 have shown that 6 is homodimeric in THF and that, in the presence of 2, it forms a novel heterodimer 10. This heterodimer is found to be the dominant reagent in the initial state, rather than the homodimer of 6. Computational investigations with PM3 and B3LYP/6-311 + G(d,p) have shown possible structures of the heterodimers, as well as the role of THF and I in the solvation of the dimers. The results are in line with the NMR results. Favoured complexes in the equilibria between homo- and heterocomplexes are also reported.
A convenient stereoselective route to the sex pheromone of the red bollworm moth via an allylic sulfenate to sulfoxide rearrangement
Aus 1-Brom-8-octanol (Ia) erhalt man nach Veretherung zu (Ib) uber eine Grignardreaktion mit dem trans- Crotonaldehyd (II) das Addukt (III), aus dem nach Dehydratisierung und Isomeri- sierung der Doppelbindung unter Verwendung von 2,4-Dinitrobenzolsulfenylchlorid das Dien (IVa) erhalten wird.