Organocatalytic trans Phosphinoboration of Internal Alkynes

Abstract

We report the first trans phosphinoboration of internal alkynes. With an organophosphine catalyst, alkynoate esters and the phosphinoboronate Ph2P‐Bpin are efficiently converted into the corresponding trans‐α‐phosphino‐β‐boryl acrylate products in moderate to good yield with high regio‐ and Z‐selectivity. This reaction operates under mild conditions and demonstrates good atom economy, requiring only a modest excess of the phosphinoboronate. X‐ray crystallography experiments allowed structural assignment of the unprecedented and densely functionalized (Z)‐α‐phosphino‐β‐boryl acrylate products.

Inter‐Element Boration Reactions of Carbon‐Carbon Multiple Bonds via Lewis‐Basic Activation of Boron Reagents

“…Wescott and Santos employed Ph 2 P−Bpin, originally developed by Westcott, [55] in the phosphinoboration of alkynoates with the aid of catalyic tributylphosphine (Scheme 33). [56] They propose that the mechanism of this reaction is basically the same as that of their hydroboration reaction. A wide range of α‐phosphino‐β‐borylamides can be obtained in moderate yield when R 1 is an aryl group.…”

Recent Advances in Organophosphorus‐Catalyzed Borylation and Silylation Reactions

“…Recently, Santos and coworkers pioneered a highly regioselective phosphine‐catalyzed anti ‐phosphinoboration of internal alkynes 57 to afford α‐phosphino‐β‐boryl acrylates 58 in 11–72% yields and 53:47‐96:4 Z : E selectivity (Scheme 21). [19] Several alkyls, aryl, and heteroaryl groups on alkynoate esters with electron‐donating groups and halogen substituents were converted to the corresponding borylated products in good yields and stereoselectivities. However, alkynoate 58 g bearing electron‐withdrawing acetyl group underwent phosphinoborylation with poor yield (27%; Z : E 93:7).…”

Organocatalytic trans Phosphinoboration of Internal Alkynes

“…The trans selectivity of the reaction was confirmed by the X-ray structure of 2 f, where the orientation of phosphorus (P1) and boron (B1) is clearly in the Z configuration (Figure 1). [22] In contrast with amide counterparts, [20e, 23] internal coordination between boron and carbonyl oxygen is negligible (2.397 ).…”