Preparation of optically active flowery and woody‐like odorant ketones via Corey‐Chaykovsky oxiranylation: Irones and analogues

Abstract

α‐, β‐, and γ‐Irones and analogues have been prepared from optically active ketones (+)‐1, (+)‐6a,b, and (+)‐17, via a Corey‐Chaykovsky oxiranylation (Me2S, Me2SO4, Me2SO, NaOH) followed by isomerisation (SnCl4 or MgBr2). (+)‐Dihydrocyclocitral (19a), obtained from (−)‐citronellal, and analogue (+)‐19b, were condensed with various ketones to afford (+)‐21a–f, and after hydrogenation (+)‐22a–f. A mild oxidative degradation of aldehydes (+)‐trans‐and (−)‐cis‐8a,b, to ketones (−)‐16a,b, as well as olfactive evaluations, 13C‐NMR assignments, and absolute configurations of the intermediate epoxides, aldehydes, and alcohols are presented.

In the Quest for a Virtual Pseudo Receptor for Sandalwood‐Like Odorants. Part I

“…Alternatively, an intermediate connectivity of the O-atom was generated from ketone (À)-(R)-21 via a CoreyÀChaykowsky oxiranylation [65], leading to the corresponding 1.3 : 1 mixture of epoxides (À)-(R)-25 (Scheme 6). This mixture was isomerized in the presence of BF 3 ¥ OEt 2 [66] to thermodynamically afford the epimerized equatorial aldehyde (À)-(R)-26a under basic conditions (MeONa/MeOH, reflux). Reduction with LiAlH 4 furnished a primary trans-alcohol (À)-(R)-27a, while Me-Grignard addition afforded the analogous secondary trans-alcohol (À)-(R)-27b as a 1 : 1 mixture.…”

Enzyme-Mediated Preparation of the Single Enantiomers of the Olfactory Active Components of the Woody OdorantTimberol®

“…The GC analyses of the acetate derivatives of 6 recovered from the less soluble 4-nitrobenzoate (three crystallizations from MeOH) and from the mother liquor are reported in the Figure. The racemic alcohol diastereoisomer recovered from the crystalline 4-nitrobenzoate ( Fig.,b, 3rd and 4th GC peaks) provided, upon acetylation in the presence of lipase PS, the (1'R,3R,6'R)-acetate 8 (Fig.,c) and (1'S,3S,6'S)-alcohol 6a (Fig.,d) which were separated by CC (SiO 2 ). The configurational assignment shown in Scheme 1 was based on the conversion of 8 into the known [11] unsaturated ketone 9 by basic hydrolysis and MnO 2 oxidation, and of 6a into (1'R,3S,6'S)-alcohol 3a (cf. [7]), showing an extremely pleasant powdery woody odour, by catalytic hydrogenation (H 2 , PtO 2 , AcOH).…”

Synthesis of Citronellal by RhI-Catalysed Asymmetric Isomerization ofN,N-Diethyl-Substituted Geranyl- and Nerylamines or Geraniol and Nerol in the Presence of Chiral Diphosphino Ligands, under Homogeneous and Supported Conditions

“…Under these conditions, the ligand (R)-6 exhibited very similar reactivity and selectivity, even at 0.25 mol-% of the catalyst (i.e. of the ligand) for both diethylgeranylamine ((E)-1) [21] and diethylnerylamine ((Z)-1) [22] 7 ) when compared to (R)-5 used under homogeneous conditions (see Table 1, Entries 1 and 2). The ratio (R)-6/(E)-1 could even be decreased to 0.1 mol-% without affecting either the conversion or the enantioselectivity 8 ).…”

“…This methodology has also been successfully extended to the preparation of ()-7-hydroxyor ()-7-methoxycitronellal [6]. The acidic cyclization of the (À)-antipode (S)-4 to ()-(1R,6S)-trans-dihydrocyclocitral [7] 2 ) is also fundamental for the synthesis of ()-norlimbanol [10] 3 ), as well as of optically pure dihydroionone [7] and dihydrodamascone analogues [12a]. (À)-Citronellal ((S)-4) has also been used as a potential starting material for the synthesis of (À)-(2S,4R)-rose oxide [12b,c].…”

“…GC Retention times of (À)-(S)-and ()-(R)-isocitronellal are t R 37.8 and 38.1 min, respectively, under the conditions used for the analyses of 4 (see Footnote6). This aldehyde does not influence the subsequent enol acetate acid-mediated cyclization step, since an identical carbocation is generated[7] [8][10].…”