Palladium(0)/Copper(I)‐Catalyzed Tandem Cyclization of Aryl 1‐Cyanoalk‐5‐ynyl Ketone System: Rapid Assembly of Cyclopenta[b]naphthalene and Benzo[b]fluorene Derivatives

Abstract

We have developed a new and general approach to construct a variety of benzo[b]fluorene and cyclopenta-[b]naphthalene derivatives via the palladium(0)/copper(I)-catalyzed tandem cyclization of aryl 1-cyanoalk-5-ynyl ketone systems in an extremely efficient manner. The key operation lies in the copper(I)-catalyzed aerobic oxidation, which allows for activation of two successive intramolecular cycloadditions immediately after the Sonogashira coupling reaction has occurred.

The Total Synthesis of Retrojusticidin B, Justicidin E, and Helioxanthin

“…4b,14 In continuation of our studies on the synthesis of natural and unnatural lignan for new drug screening, we have developed several efficient cyclization processes to have facile access to linear [6,6,5] or [5,6,5] tricyclic systems (Scheme 1). [15][16][17] These protocols are currently extended to the synthesis of various natural products containing either cyclopenta [b]naphthalene or benzo [b]fluorene skeletons, such as stealthins and kinamycins. 18 In addition, it was discovered that instead of using α-cyano ketones as substrates, Encouraged by the success of the model study, the synthesis of retrojusticidin B was then attempted following the similar approach starting from alkynol 5, commercially available or readily prepared according to the procedure reported in the literature.…”

Facile synthesis of indene and fluorene derivatives through AlCl3‐catalyzed cyclization of in situ formed iminium ions

“…The reason for this phenomenon is unclear, we think that the electronic properties and the coordination abilities of these substrates should be responsible for the observed results . In addition, 1‐naphthyl and 2‐naphthyl substituted acroleins 1m and 1n can also be applied to this reaction, providing a facile method to access benzene‐fused indene type of tricycles ( 3m–n) , which are also useful carbocyclic skeletons . To our disappointment, aromatic and cinnamic ketones such as ( E )‐3‐methyl‐4‐phenylbut‐3‐en‐2‐one and 2‐acetyl‐bipheny can not undergo this transformation even under harsh reaction conditions, which can probably be attributed to the lower electrophilicity of the ketone.…”

Manganese(III)‐Catalyzed Oxidative Cyclization of Aryl 1‐Cyanoalk‐5‐ynyl Ketone Systems: A Convenient and General Approach to Cyclopenta[b]naphthalene Derivatives

“…The success in converting the title system capped with an ester, TMS or aryl group on the alkyne terminus into the corresponding cyclopenta[ b ]naphthalene derivatives under Mn(OAc) 3 ‐mediated oxidation further motivated us to broaden the scope of substrates containing more different functionalities. Along these lines, as illustrated in Figure 1, substrates capped with amide ( 9a – f ), ketone ( 9g – l ), phosphonate ( 9m – o) , and halogen ( 9p – r ) groups were then prepared via a synthetic procedure similar to Scheme 4,12…”

“…α‐Cyano ketones 1 (Scheme ) are found to undergo tandem cyclization with ease to afford the corresponding cyclopenta[ b ]naphthalene derivatives 2 under the reaction conditions ( a ) or ( b ) previously developed by us 3,4…”