Copper‐Catalyzed Direct and Stereoselective Synthesis of Conjugated Enynes from α‐Allenols

Abstract

A novel strategy for the stereoselective synthesis of conjugated enynes directly from aallenols has been developed. The reaction proceeds with perfect E-selectivity and exhibits high functional group compatibility. This catalytic system can also be applied to the stereoselective synthesis of conjugated dienynes and enediynes.

Lewis Acid Enhancement of Gold Catalytic Activity Through Counterion Coordination. Synthesis of Benzofulvenes from Progargylsilanes and Benzophenones

“…Next, hydrogen abstraction, with formation of trimethylsilanol, could lead to enyne intermediate III. At this point, equilibrium between enyne III and allene IV intermediates could occur, [20] allowing free rotation of the single bond, which should explain the regioselectivity of the reaction in terms of the differences in nucleophilicity between the two arene rings. Cationic gold allenyl intermediate IV could next experiment ring-closure through a Nazarov-type reaction, [21] leading to formation of benzofulvene skeleton V. From intermediate V, consecutive rearomatization and protodeauration steps could give rise to silyl benzofulvene intermediate VI.…”

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

“…Zwitterionic allenyl copper species Cu- 270 and Cu- 270′ are proposed as intermediates in the observed alkene isomerization. 220 …”

“…Further Z-E isomerization experiments on Z -enyne 266a′ under similar reaction conditions showed that formation of the observed E -enynes 266 should be thermodynamically controlled (Scheme , reaction b). Zwitterionic allenyl copper species Cu- 270 and Cu- 270′ are proposed as intermediates in the observed alkene isomerization …”

“…Zwitterionic allenyl copper species Cu-270 and Cu-270′ are proposed as intermediates in the observed alkene isomerization. 219 Enynes have been also proposed as reaction intermediates in the transformation of allenols into the 2H-pyran-2-one skeleton, or into substituted benzene rings. 3-Hydroxy-4,5-dienoates 271 can be converted into differently substituted pyranones 272 under protic acid catalysis.…”

TfOH-Catalyzed Phosphinylation of 2,3-Allenols into γ-Ketophosphine Oxides

“…Over the past several years, 2,3-allenols and their derivatives have been employed as structurally diverse and fascinating building blocks for the construction of CC and CX bonds, as well as for the preparation of a wide range of valuable molecular frames in modern organic synthesis, such as dihydrofurans, lactams, enynes, 2-pyrrolines, carbazoles, and furanones . Inspired by these precedents and our recent work on CP bond formation, we disclosed the first example of a single-step and selective synthesis of structurally diverse γ-ketophosphine oxide frameworks via a simple and efficient Brønsted acid-catalyzed direct phosphinylation of unprotected 2,3-allenols under metal-free and additive-free conditions with remarkable functional group tolerance, high regioselectivity, complete atom-economy, and moderate to excellent yields (Scheme d).…”