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Synthesis of Functionalized Hydropentalenes by an Asymmetric Deprotonation/Alkylation Strategy
Author(s) -
Lutz Vanessa,
Baro Angelika,
Fischer Peter,
Laschat Sabine
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200901154
Subject(s) - alkylation , deprotonation , chemistry , electrophile , enol , enantioselective synthesis , alkyl , medicinal chemistry , halide , silylation , acetal , enol ether , silyl enol ether , ether , amide , stereochemistry , organic chemistry , catalysis , ion
The functionalization of differently substituted hydropentalenone derivatives 9 , derived from the Weiss diketone ( 8 ) by enantioselective deprotonation in the presence of lithium ( R , R )‐bis(1‐phenylethyl)amide/LiCl ( 11· LiCl) as the chiral base is described. In the first route the resulting enolate was treated directly with alkyl halides as electrophiles to give the target α‐alkylhydropentalenones 12 , whereas in the second route the enolate was trapped as one of the triethylsilyl enol ethers 17 , from which the enolate was regenerated by treatment with MeLi prior to alkylation with alkyl halides. The substituents on 9 seemed to influence which strategy is favored: for the OTBS‐substituted hydropentalenone 9a the direct deprotonation/alkylation is preferred, whereas for the acetal‐substituted hydropentalenone 9b the silyl enol ether route is more suitable. In all cases the α‐alkylated hydropentalenones 12 and 15 were isolated with good diastereoselectivities.