Rhodium-Catalyzed Asymmetric Hydroboration/Cyclization of 1,6-Enynes Enabled by Spirosiladiphosphine Ligands: Constructing Chiral Five-Membered Rings with a Boron Handle

Abstract

A rhodium-catalyzed enantioselective hydroboration/cyclization reaction of 1,6-enynes is achieved by employing a spirosiladiphosphine ligand. The process allows the synthesis of five-membered hetero-and carbocycles bearing a boron handle with high levels of activity and selectivity. Various enynes and organoboranes (HBdan, HBpin, HBmp, and HBamm) have been accommodated, and enynes containing terminal alkynes have been integrated into the process for the first time. The high yields and selectivities of the transformation highlight the synthetic utility of these novel spirosiladiphosphine ligands. R hodium-catalyzed asymmetric cyclization of 1,6-enynes has emerged as a powerful and atom-economical approach to generate chiral hetero-and carbocycles. 1 This process often integrates additional transformations, such as hydrogenation and hydrofunctionalization, to facilitate consecutive C−X and C−C bond-forming events (Scheme 1A). 2 In this line, Ojima 3 first reported the hydrosilative cyclization of 1,6-enynes. Subsequent contributions from Chung, 4 Widenhoefer, 5 Zhou, 6 and others 7 have enabled the reaction to proceed with enhanced efficiency and superior enantiocontrol.

Highly enantio- and diastereoselective construction of spirocyclic oxindoles via a palladium-catalyzed decarboxylative asymmetric [4 + 2] annulation strategy

“…Encouraged by this impressive result, a series of chiral bisphosphonate ligands were screened, including substituted spirodiphosphine skeletons L4–L5 , Segphos scaffolds L6–L7 and Binap backbones L8–L11 (entries 4–11). The chiral spirosiladiphosphine ligand L5 , 8 which has a spiro silicon atom substituent and significantly larger P–M–P bite angle than spirodiphosphine, resulted in a lower yield and enantioselectivity for the desired product 3a (38% yield, 5% ee, entries 4 and 5). In contrast, better yields and stereoselectivities were observed for the reactions with Segphos L6 (Table 1, entry 6).…”