Electrocyclic reactions of tetraenes

Shimalactone Biosynthesis Involves Spontaneous Double Bicyclo‐Ring Formation with 8π‐6π Electrocyclization

“…Further biomimetic synthetic studies were reported for SNF4435 C and D by the Baldwin group and Trauner et al., respectively. Since octatetraenes undergo 8π electrocyclization at room temperature with low activation barriers, followed by 6π electrocyclization, formation of the bicyclo[4.2.0]octadiene skeleton is considered to occur spontaneously without enzymatic assistance. Indeed, neoaureothin (spectinabilin), a nitroaryl‐substituted tetraene compound, was shown to be converted non‐enzymatically into SNF4435 C and D by photoinduced tetraene isomerization followed by an 8π‐6π electrocyclization cascade .…”

A palladium-mediated cascade cyclisation approach to the CDE cores of rubriflordilactone A and lancifodilactone G

“…Hexacycle 20 likely arises from an initial 6p-electrocyclisation to form a spirocyclic 7,6-ring system 22, which then undergoes an intramolecular Diels-Alder reaction with the proximal exo-methylene group, again driven by restoration of aromaticity to the furan. This mode of cascade cyclisation was initially discovered by Marvell et al, 21 and has undergone a revival in the context of the pyrone-polypropionate natural products. 22 The formation of tetracycle 18 and tricycle 21 (the latter containing the targeted lancifodilactone CDE core) can be rationalised by an initial thermal isomerisation of 19, followed by 8p-cyclisation; the intermediate cyclooctatriene then undergoes either 6p-cyclisation to give 18, or a 1,5-hydride shift to tricycle 21.…”

Thermal reaction of [3,4]-benzo-8-substituted-3Z,5Z,7E-octatetraenes and quantum-chemical study of the (8π,6π)-electrocyclisation

“…10 Thermolysis of several cyclooctatraene derivatives following the 8p,6p electrocyclization reaction mechanism has been reported in the literature, and in all cases configuration around the double bonds was found to be crucial for reactivity. 11, 12 Typical examples are provided by compounds 1 13 and 2 6,7 (Chart 1). In molecules 1 and 2 in which substituents are attached at the termini of tetraene moiety 8p,6p-electrocyclization readily takes place.…”

“…Chart 1 Literature examples of octatetraene systems 1-3 undergoing 8p,6p electrocyclisations. [13][14][15][16] As a part of our longstanding interest in intramolecular photocycloaddition reactions of heteroaryl substituted hexatrienes 4 (n = 1, Chart 2) with one double bond incorporated into the benzene ring 17 we recently reported synthesis and photocycloadditions of novel o-butadienylstyrenes 5 (n = 2). 18 In continuation of this work we here present results of experimental and computational study 19 of thermal reactions of the latter compounds.…”