Enyne-2-pyrone [4 + 4]-Photocycloaddition: Sesquiterpene Synthesis and a Low-Temperature Cope Rearrangement

Abstract

Intramolecular [4 + 4] photoreaction of 2-pyrones with a 1,3-enyne yields an unstable 1,2,5-cyclooctatriene product. Without a C4 pyrone substituent, 1,3-hydrogen migration converts the allene to a 1,3-diene, with a skeleton related to dactylol. With methoxy substitution, Cope rearrangement yields a nine-membered ring fused to a cyclobutane. Both structures were confirmed by X-ray crystallography. The Cope rearrangement is apparently reversible, reforming the allene which undergoes a proton shift to the more stable 1,3-diene product.

Recent Advances in the Total Synthesis of Natural Products Containing Eight-Membered Carbocycles (2009–2019)

“…Because of their fascinating structures and biological importance, natural products containing eight-membered rings have attracted considerable attention from the synthetic community. Nowadays, numerous methodologies have been developed to construct eight-membered ring systems, some of which were reported very recently, − and many of which have also been applied to total synthesis of cyclooctanoids. Nevertheless, more practical, flexible, and efficient strategies to synthesize eight-membered rings are still required.…”

Novel, male-produced aggregation pheromone of the cerambycid beetle Rosalia alpina, a priority species of European conservation concern

“…To achieve deoxygenation at C-4 of the pyrone ring, the hydroxypyrone 4 was first converted to triflate 5 . When the reaction was carried out with triflic anhydride and triethylamine in CH 2 Cl 2 [ 74 – 76 ], the desired product 5 was formed along with a minor amount of its regioisomer 5b [ 74 ], and the ratio of 5 / 5b appeared to be dependent on the purity of the triflic anhydride ( Fig 6 ). However, reaction of 4 with N -phenyl-bis(trifluoromethanesulfonimide) in the presence of potassium carbonate in THF at 60°C [ 77 ] proved to be much cleaner and more reliable, producing 5 as the only product in excellent yield ( Fig 5 ).…”

“…However, reaction of 4 with N -phenyl-bis(trifluoromethanesulfonimide) in the presence of potassium carbonate in THF at 60°C [ 77 ] proved to be much cleaner and more reliable, producing 5 as the only product in excellent yield ( Fig 5 ). Finally, reduction of triflate 5 with triethylsilane and Pd catalysis gave deoxygenated target compound 6 in excellent yield [ 74 , 76 ].…”

Me2(CH2Cl)SiCF3 Facilitated Tandem Synthesis of Oxasilacycles Featuring a Trifluoromethyl Group

“…The development of efficient methods for the facile synthesis of structurally diverse oxasilacycles is of current interest. Four major synthetic strategies have been established, including the following: the Si–O bond formation of hydroxysilanes, the C–O bond formation of silanols, the Si–C bond formation of silyl ethers, and the C–C bond formation of silyl ethers . Despite significant progress, facile construction of fluorine-containing oxasilacycles remains underdeveloped, although they have exhibited promising properties for various applications, as shown by the trifluoromethylated oxasilacycles such as Martin’s spirosilane ( A ) , or reusable silicon-based transfer agent ( B ) for cross-coupling reaction.…”