Palladium-Catalyzed Asymmetric Synthesis of Axially Chiral Allenylsilanes and Their Application to S_E2′ Chirality Transfer Reactions

Abstract

Stepwise application of the Pd-catalyzed S(N)2' reaction and the desilylative S(E)2' reaction to the ambivalent 2-bromo-1-silyl-1,3-dienes provides a novel route to the highly enantioselective construction of tertiary and quaternary propargylic stereogenic centers via axially chiral allenylsilanes.

Atropisomerism and Axial Chirality

“…Axial-to-central chirality transfer of allenylsilanes to alkynes has also been reported. 69 Electrofilic fluorination of enantioenriched allene 84 with Selecfluor afforded propargylic fluoride 85 in 94% ee in 77% yield (Scheme 36). Reaction of allene 84 with propanal dimethylacetal at −78°C in the presence of TiCl4 gave a (4:1) diastereomeric mixture of homopropargylic methyl ethers 86 in 73% and 94% ee (Scheme 36).…”

2.05 Propargyl and Allenyl Organometallics

“…47 In addition to the two aforementioned studies, Ogasawara and Takahashi reported a catalytic asymmetric methodology to synthesize chiral allenylsilanes (Scheme 27, Table 43). 48 Table 44). 49 The presence of the silyl moiety was shown to be crucial; cyclohexyl derivative 128 provided the highest yields of cross-over product presumably due to steric factors.…”

Synthesis of Natural Products with Polycyclic Systems

“…To overcome this, we employed a chirality transfer from an allenylsilane. [22][23][24][25] Requisite allenylsilane 19 was prepared in an optically active form via an asymmetric reduction of a ketone under Noyori transfer hydrogenation conditions [26][27][28][29] and an S N 2′ reaction with a Lipshutz reagent. 30) Treatment of allenylsilane 19 with paraformaldehyde in the presence of TiCl 4 ·2THF afforded homopropargyl alcohol 20 in 52% yield.…”