Recent Advances and Perspectives in Transition Metal‐Catalyzed 1,4‐Functionalizations of Unactivated 1,3‐Enynes for the Synthesis of Allenes

Abstract

Classic methods for the synthesis of allenes usually introduce only one functional group into products. In this review, we highlight the recent advances and perspectives in the synthesis of allenes by transition metal‐catalyzed 1,4‐functionalization of unactivated 1,3‐enynes.

Silylboranes as Powerful Tools in Organic Synthesis: Stereo- and Regioselective Reactions with 1,n-Enynes

“…Addition of silylboranes to 1,3-enynes can proceed by either 1,2-or 1,4-cis-addition to give 1,3-and 1,2-dienes, respectively; 12a,40 transition-metal-catalyzed 1,4-functionalization of 1,3-enynes in fact serves as a powerful strategy for the synthesis of multisubstituted allenes. 41 The mode of addition is a function of the nature of the alkyne substituent, 40 but as a rule 1,2-addition occurs to give the cis-1,2functionalized 1,3-diene product (Scheme 7). 42 Reactions of 1,3-enynes with PhMe 2 SiB(pin) catalyzed by Pd(0) complexes, generated from Pd(acac) 2 , a phosphine or phosphite [such as PPhMe 2 , PEt 3 , P(OEt) 3 ] and DIBAL-H, are highly regioselective for terminal and non-terminal alkynes, but lead to mixtures of regioisomers for substrates with a terminal olefinic bond.…”

Halogenated salt assisted Cu-catalyzed asymmetric 1,4-borylstannation of 1,3-enynes: enantioselective synthesis of allenylstannes

“…Transition metal-catalyzed 1,4-functionalizations of unactivated 1,3-enynes is becoming a valuable and straightforward option to prepare allenes, 4 mainly because of the ready availability of the starting materials, and two (mostly, different) functional groups can be installed for the construction of more complex multisubstituted allenes in a step-economic way. However, to date, the majority of reported methods have focused on racemic versions and there are only sporadically successful examples of asymmetric catalysis.…”

Palladium-catalyzed allene synthesis enabled by β-hydrogen elimination from sp2-carbon

“…The active nature imparted by its unique orthogonal cumulative π -system also makes them highly versatile and useful building blocks in organic synthesis 15 – 19 . Although numerous methods for the preparation of allenes have been developed 20 – 24 , they still lag far behind the growing demand in the application. At present, the majority of the existing methodologies rely on the utilization of elaborate alkynes.…”