Chiral building blocks based on technical grade β-citronellene

Abstract

+)-j-Citronellene, the main component of the %ecbnical grade pyrolysate of (+)-cis-pinane, can be chemoselectively processed to certain C10 derivatives in the presence of isomeric Clo olefins. These derivatives are converted into mono-and bifunctional chiral building blocks suitable for the incorporation of4deCH.Y fragments with 8-or &con-figuration into aliphatic chains. Although their optical purity may be as low as 50%, that o f the end prQducts can be upgraded by inclusion of an optical resolution step in the synthetic sequence.

Thermal Isomerization of (+)‐cis‐ and (−)‐trans‐Pinane Leading to (−)‐β‐Citronellene and (+)‐Isocitronellene

“…Whereas 2 and 3 seem to arise from a fragmentation of the cyclobutane ring in 1 (path I and II; Scheme 3), the formation of p-menthenes 6-8 can be explained by using a biradical pathway combined with Hshift reactions [1,5] according to the formation of limonene from a-or b-pinene (path III; Scheme 5). [4,5,[8][9][10][11] Two possible mechanisms for the fragmentations of fourmembered rings (cyclobutane, oxetane) are discussed in the literature.…”

“…[4,8,10,33] According to the formation of 2 from 1 a and 1 b, the initial formation of a 1,4-carbon-centered biradical (BR1; cf. Scheme 3) by bond breakage between C 1 and C 6 is necessary for the side-reaction pathway leading to 6-8. p-Menthenes 6-8 are formed by [1,5]Hshifts, in which the hydrogen migration from C 9 to C 2 yields those isomers with the exocyclic double bond. The reaction route by a hydrogen shift from C 1 to C 8 leading to 8 is suppressed in favor of the formation of 6 and 7 due to the higher selectivity (cf.…”

“…[9] All of these isomerization reactions of bicyclic pinane-type compounds yield at least one acyclic Abstract: Catalyzed and uncatalyzed rearrangement reactions of terpenoids play a major role in laboratory and industrial-scale synthesis of fine chemicals. Herein, we present our results on the thermally induced isomerization of pinane (1). Investigation of the thermal behavior of (+)-cis-(1 a) and (À)-trans-pinane (1 b) in a flow-type reactor reveals significant differences in both reactivity and selectivity concerning the formation of (À)-b-citronellene (2) and (+)-isocitronellene (3) as main products.…”

“…limonene, b-citronellene (2), a-pinene, b-pinene) and terpenoids, such as 2-pinanol or citral, play an important role in the industrial synthesis of flavors and fragrances. [1][2][3] They are valuable chiral building blocks for the synthesis of ligands and natural products, and they are important chiral auxiliaries. The thermal isomerization of bicyclic terpenes with the pinane skeleton (1; Scheme 1) yields acyclic isomers and p-menthane-type monocyclic terpenes.…”

Kinetic and mechanistic aspects of myrcene production via thermal-induced β-pinene rearrangement

“…flavors, fragrances, pharmaceuticals) [1][2][3][4][5][6]. Using aor b-pinene (1) as starting materials for chemical syntheses is advantageous considering sustainability and environmental impacts, because these are widely available and can be obtained from natural resources by distillation of turpentine or crude sulphate turpentine (CST) [1][2][3].…”