Dragoco Gerberding & Co AG

C21H24N2O6, orthorhombic, P212121 (No. 19), a = 6.285(2) Å, b = 9.044(4) Å, c = 35.52(2) Å, V = 2019.0 Å3, Z = 4, R(F) = 0.095, wRref(F2) = 0.279, T = 295 K.

3-Mercapto-2-methylpentan-1-ol was first detected in a complex thermally processed flavor and finally isolated from raw onions. The chemical structure of this new compound was identified by MS and (1)H NMR measurement and synthesis of the proposed structure. Sensory evaluation at different concentrations indicated that the flavor quality is strongly dependent on concentration. At low concentration (0.5 ppb) a pleasant meat broth, sweaty, onion, and leek-like odor can be perceived. On the basis of some isolation experiments and volatiles occurring in raw onions, a formation pathway is proposed. As one intermediate 3-mercapto-2-methylpentanal, another new strong flavor compound, was suggested. The presence of this compound in raw onions was confirmed by synthesis and comparison of MS and chromatographic data.

Double stereocontrol is achieved in the Pd-catalyzed cyclization of Δ³ -oxonene precursors (see reactions outlined below). The configuration of the olefinic double bond and of the allylic carbon center α to the ether oxygen atom is dictated by the configuration of the double bond in the starting compound (E/Z), the Pd ligand (dppe = Ph₂ PCH₂ CH₂ PPh₂ ), and the reaction time.