A Study of the Thermal Cyclization of 1,7-Alkadienes and Monocyclic Dienes¹

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

“…Whereas products with structures similar to 5 are known from various analogous compounds of 2 (b-citronellene, isocitronellene, linalool; Table 2), substituted products with cycloheptene skeleton (6) yield from the rearrangement of 2 only [11,23,28]. Studying the thermal rearrangement of various 1,6-dienes with hydrogen in aposition, the generation of cyclopentane-type products is known to occur [12][13][14]28,[32][33][34][35][36][37][38][39][40][41]. For instance, the thermal treatment of linalool yields 1,2-dimethyl-3-isopropenylcyclopentanol (Table 2) [28,38], and consecutive reactions of the acyclic main product from the pyrolysis of nopinone lead to the formation of 2-methyl-3-isopropenylcyclopentanone (Table 2) [12,13,35,36].…”

“…For instance, the thermal treatment of linalool yields 1,2-dimethyl-3-isopropenylcyclopentanol (Table 2) [28,38], and consecutive reactions of the acyclic main product from the pyrolysis of nopinone lead to the formation of 2-methyl-3-isopropenylcyclopentanone (Table 2) [12,13,35,36]. The cyclization of 1,7-dienes with a-hydrogen leads to the formation of substituted cyclohexenes, whereas the ring-formation of systems with fused rings failed [32,33]. The cyclization proceeds via concerted ene-type reaction ( Table 2).…”

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

“…According to other 1,6-dienes (2, myrcene, linalool) the formation of 5 also proceeds by ene-type cyclization (Scheme 7). [4,5,9,13,15,34,35] The presumptive transition state leading to the formation of 5 b reveals no repulsive diaxial interactions of methyl groups, explaining the high selectivity. …”

“…The cyclization of 1,7-dienes with a hydrogen lead to the formation of substituted cyclohexenes, whereas the ring formation of systems with fused rings failed. [34,35] The cyclization proceeds by a concerted ene-type reaction (Scheme 6). [36] It is obvious, that the configuration of the chiral center in 2 remains unchanged during the reaction.…”

Intramolekulare En-Reaktionen in der organischen Synthese

“…Die bemerkenswert milden Bedingungen, unter denen sich aktivierte Enophile intramolekular an Ene addieren, z. B. bei den Reaktionen (30)- (31) und (51)+ (52), sind der gleichen Ursache zuzuschreiben.…”