Gold(I)‐Catalyzed Synthesis of Indenes and Cyclopentadienes: Access to (±)‐Laurokamurene B and the Skeletons of the Cycloaurenones and Dysiherbols

Abstract

The formal (3+2) cycloaddition between terminal allenes and aryl or styryl gold(I) carbenes generated by a retro‐Buchner reaction of 7‐substituted 1,3,5‐cycloheptatrienes led to indenes and cyclopentadienes, respectively. These cycloaddition processes have been applied to the construction of the carbon skeleton of the cycloaurenones and the dysiherbols as well as to the total synthesis of (±)‐laurokamurene B.

Generation of Gold(I) Carbenes by Retro‐Buchner Reaction: From Cyclopropanes to Natural Products Synthesis

“…Aryl gold(I) carbenes generated by retro‐Buchner reaction can also engage in a formal (3+2) cycloaddition with allenes to give rise to indenes . Indenes are important motifs present in many relevant natural products, and are also used as building blocks for organic synthesis or organometallic chemistry…”

“…The reaction of 7‐aryl‐1,3,5‐cycloheptrienes with 1,1‐dialkylallenes at 120 °C in the presence of 5 mol % of [(JohnPhos)Au(MeCN)]SbF 6 gives rise to a very wide range of highly substituted indenes in moderate to good yields . The reaction is general and tolerates substituents of different nature in the transferred aryl moiety, or even different aromatic units such as naphthalenes or phenanthrenes.…”

Gold(I)‐Catalyzed Synthesis of Indenes and Cyclopentadienes: Access to (±)‐Laurokamurene B and the Skeletons of the Cycloaurenones and Dysiherbols

“…ADiels-Alder reaction between 7g and maleic anhydride led to the crystalline endo adduct 12 in excellent yield (Scheme 2). TheX -ray diffraction structure of 12 [16] allowed confirmation of the structures assigned to 7a-k (Table 4). [a] Reaction conditions: 1a (0.1 m in DCE), 5a (2.0 equiv), catalyst (5 mol %), 120 8 8C, 8h.…”

“…Themajor isomer displayed the configuration of cycloaurenones,a ss hown by X-ray diffraction. [16] Finally, oxidative deprotection of the methoxy groups with cerium ammonium nitrate (CAN) and pyridine-2,6-dicarboxylic acid N-oxide (Py*O) [24] led to quinone 17 a.Bythe same sequence of reactions, 16 b,c orresponding to the tetracyclic carbon skeleton of the dysiherbols,w as obtained as a1:1 mixture of epimers through ar emarkably efficient radical cyclization of 15 b (81 %yield). [23] Oxidation of 16 b as before provided 17 b.…”

“…This reaction is perfectly suited for the preparation of spiro compounds,such as 6m-p and 6t.T he structure of indenes 6d, 6t,and 6u was confirmed by single-crystal X-ray diffraction. [16] Although the resulting indenes have ar eactive double bond, 2:1a dducts were only observed as very minor products in the crude reaction mixtures.I nc ontrast, a2:1 adduct was obtained in the reaction of 1-cyclohexylallene 5h,amonosubstituted allene,w ith 1a to form 11,w hose relative configuration was determined by X-ray diffraction. [16] Styryl cycloheptatriene 2a reacted with allene 5a to give cyclopentadiene 7a in 50 %y ield in the presence of gold(I) complex B (5 mol %) in EtOAc at 100 8 8C ( Table 3).…”