No abstract

~ ~~The transformation of 36 bis(homoallylic) alcohols VIl to alkenones IX and X via /I-cleavage of their potassium alkoxides VIIa in HMPA has been investigated (cf. Scheme 2). These studies have established an order of /]-cleavage for 2-propenyl, l-methyl-2-propeny1, 2-methyl-2-propeny1, 1, I-dimethyl-2-propeny1, and benzyl groups in alkoxides 49a-56a and have allowed a comparison between the /I-cleavage reaction and the oxy-Cope rearrangement in alkoxides 74a 83a. As illustrative synthetic applications, a two-step preparation of propenyl ketoncs 1 5 4 2 from carboxylic esters is dcscribcd, together with syntheses of' or-turmerone (48), cc-damascone ((E)-71), a-damascone ((E)-109) and /I-damasccnone ((I?)-1 11).

Starting from the γ‐lactone cis‐1, two new syntheses of γ‐damascone ((E)‐4) are described. In both syntheses, the key step involves the β‐cleavage of a bis(homoallylic) potassium alkoxide, viz. the transformation of 3a to 20 and (E/Z)‐4, and the conversion of 21a to 23 and (E/Z)‐24.

Several chicken parts (skin, fat, juice) were cooked in different ways (roasting, simmering) and investigated separately for their volatile composition. In-depth GC/MS analysis of the separate fractions revealed several unknown molecules. Mass spectra interpretation allowed us to identify nine molecules for the first time in chicken, including cyclic aldehydes, cyclic ketones, and new δ-lactones containing an unsaturated linear chain. Identification was confirmed by chemical synthesis followed by comparison of the mass spectra and linear retention indices. The natural occurrence of five of these molecules is reported here for the first time in a natural product.

Treatment of the unsaturated bicyclic homoallylic alcohols (E)‐ and (Z)‐5 and (Z)‐ and (E)‐10 and allenic alcohol 16 with an excess of ClSO3H in 2‐nitropropane or CH2Cl2 at − 80° afforded, in moderate yields (ca. 30–70%), diastereoisomer mixtures of racemic tetracyclic ethers 12a–c (Table 1) and 17a,b (Table 2), respectively. These kinetically controlled stereospecific transformations are believed to proceed via concerted or nonconcerted pathways (see Schemes 4 and 6) and the results are fully consistent with our earlier work. Representing novel didehydro bridged analogues of known, olfactively active labdane tricyclic ethers, the organoleptic properties of 12a–c and 17a,b are briefly described, especially those of 12c which, in the context of structure–activity studies, is a racemic didehydro analogue of the known ambergris odorant Ambrox®.