Gold-Catalyzed Cyclization/Hydroboration of 1,6-Enynes: Synthesis of Bicyclo[3.1.0]hexane Boranes

Abstract

The gold-catalyzed cyclization/hydroboration of 1,6enynes offers facile, versatile, and atom-economical one-step access to bicyclo[3.1.0]hexane boranes. This new protocol proceeds in moderate to good yields under mild conditions. Different from bicyclo[3.1.0]hexane borates, these products are stable in air and during chromatography. Moreover, the borane moiety of the products can readily undergo a diverse array of transformations. The kinetic isotope effect experiment indicates that the hydrogentransfer step is a fast process, which is not involved in the ratelimiting step.

Recent Advances in Cyclization Reactions of 1,6‐Enynes

“…In the same year, the Zhao and Wang group developed a gold‐catalyzed cyclization/hydroboration reaction of 1,6‐enynes for the construction of boryl‐ incorporated bicyclo[3.1.0]hexanes in one step proceeding through 5‐ exo ‐dig cyclization/insertion of gold carbene into the B−H bond sequences (Scheme 8). [18] This protocol, which employed IPrAuCl/AgPF 6 as catalysts, DCM as solvent, and gave corresponding products in moderate to good yields with wide functional group tolerance. In addition, these bicyclic derivatives were stable in the chromatographic analysis process.…”

Atom-economical synthesis of bicyclo[3.1.0]hexane silanes by gold-catalyzed Si–H bond insertion reaction of 1,6-enynes with hydrosilanes

“…11 Related carbene-transfer reactions have been extensively applied to the assembly of numerous carbocyclic and heterocyclic compounds. 12 In view of the important role of gold catalysis, 13 and in continuation of our interest in carbene chemistry, 14 herein, we describe a protocol for gold-catalyzed insertion of cyclopropyl gold carbene, which is produced in situ via the cycloisomerization of 1,6-enynes, into the Si–H bonds of hydrosilanes (Fig. 1c).…”

Reagent- and Ligand-Dependent Mechanistic Trichotomy in Fe-Catalyzed Borylative Cyclizations of Enynes

“…These transformations provide unique access toward structurally complex homoallylboronates or vinylboronates (Figure a). Common catalysts that have been reported to specifically deliver one of these products rely on the use of Pd, Rh, Cu, Ni, Co, or Fe complexes. − More recently, interesting new alternative borylative cyclization reactions using Pd, Ru, or Au complexes were disclosed . Treatment of proparylic allyl tosylamides with bis­(pinacolato)­diboron (B 2 pin 2 ) , or borane–amine complex led to the formation of azabicyclo[3.1.0]­hexanes, a structural motif found in a variety of biologically interesting compounds .…”