(16.111.93)Treatment of ten monocyclic dienols 8-11 with an excess of fluorosulfonic acid in 2-nitropropane at -90" afforded diastereoisomeric mixtures of racemic tricyclic ethers 12-14 in 81-91 % yield (see Tables I and 2). These transformations represent further examples of biomimetic acid-mediated cyclisations in which an OH group serves as the internal nucleophilic terminator. A non-synchronous process is postulated, and the examples described strongly re-inforce our working mechanistic hypothesis, whereby the stereochemical course of cyclisation is directed by the orientation of the side chain vicinal to the intermediate cyclohexyl cation (see Schemes 4 and 5 ) . It is also demonstrated that the efficiency of this process is independent of the nature of the OH group, which may be primary, secondary, or tertiary. In addition, the organoleptic properties of 12-14, Me homologs of known odorants such as Ambroxs ((-)-3a) and its diastereoisomers, are briefly discussed.Introduction. -Recently, we described an efficient biomimetic access to organoleptically active tricyclic ethers, by treatment of appropriately substituted 6-(cyclohexenyl)hex-3-en-1-01s with an excess of fluorosulfonic acid in 2-nitropropane at -90" [ 11. These kinetically controlled cyclisations') were shown to proceed stereospecifically via protonation of the cyclohexenyl bond, followed by ring closure involving equatorial C-C bond formation with concomitant internal nucleophilic termination by anti-addition of the OH group across the C(3)=C(4) bond. For example, allowing for partial acidcatalysed isomerisation of the C(3)=C(4) bond, (E)-and (Z)-l selectively afford 3a and 3b, whereas (E)-and (2)-2 preferentially generate 3c and 3d, oiu a favoured chair

Treatment of the unsaturated allenic alcohols (E)‐7, (Z)‐7, 10, 13, and 19 with an excess of FSO3H in 2‐nitropropane at −90° to −30° afforded, in 68–85% yield, diastereoisomer mixtures of racemic tricyclic ethers 14a–d and 20a–d, respectively (Schemes 3 and 5), with high stereoselectivity (see Table and Scheme 6). These stereospecific transformations represent the first reported examples of an acid‐mediated polyene cyclization, in which an alkene is the initiating group and an allenic alcohol serves as the internal terminator. In close analogy to our earlier work, a nonsynchronous process is postulated, whereby the stereochemical course of cyclization is directed by the conformational structure of an intermediate cyclohexyl cation (see Schemes 3 and 6). In addition, the organoleptic properties of 14c and 20c, racemic didehydro and methyl didehydro analogues, respectively, of the known odorant Ambrox® ((−)‐4f), are briefly discussed.

Es wurde die Synthese der 3‐Isopropyl‐6‐methylhomophtalsäure beschrieben. Diese Säure erhielt man durch einen oxydativen Abbau unter Ringaufspaltung mit Wasserstoffperoxyd aus dem 4‐Methyl‐7‐isoprop‐α‐indanon‐glyoxylester oder der entsprechenden Hydroxymethylenverbindung des 4‐Methyl‐7‐isopropyl‐α‐indanons. Sie konnte durch Oxydation mit KMn4 z. T. in das bekannte 3‐Isopropyl‐6‐methylphtalsäureanhydrid und z. T. in eine Säure der Bruttoformel C113H14O6 übergeführt werden.

Dedicated to Professor Georg Frµter on the occasion of his 65th birthday Treatment of the acyclic tetraenols (E)-and (Z)-2 with an excess of ClSO 3 H in 2-nitropropane at À 808 stereoselectively afforded in 30 and 43% yield, respectively, diastereoisomer mixtures of the racemic, tricyclic ethers 1c,d and 1a,b, together with 20 (Table). Under identical conditions, but with the acyclic pentaenol 10 (1 : 1 diastereoisomer mixture) as substrate, the tricyclic ethers 22a/22b (10 : 1) were isolated in 27% yield. These kinetically controlled stereospecific transformations are thought to proceed via non-concerted pathways (see Schemes 5 and 7), fully consistent with our earlier work. In contrast, another set of reaction conditions (CF 3 CO 2 H, CH 2 Cl 2 , À 158 to À 108) was used for the cyclization of the monocyclic dienols (E)-3 and (Z)-3, which resulted in the non-stereoselective formation of the major products 1c,d and 1a,b, respectively, in 35 -37% yield. Representing novel didehydro analogues of the known ambergris odorant (AE)-Ambrox and its diastereoisomers, the qualitative organoleptic properties of 1a -d and of the 10 : 1 diastereoisomer mixture of the novel tetradehydro analogues 22a/ 22b are briefly described.