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Facial‐Selective Allylation of Methyl Ketones for the Asymmetric Synthesis of α ‐Substituted Tertiary Homoallylic Ethers
Author(s) -
Tietze Lutz F,
Völkel Ludwig,
Wulff Christian,
Weigand Berthold,
Bittner Christian,
McGrath Paul,
Johnson Keyji,
Schäfer Martina
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010316)7:6<1304::aid-chem1304>3.0.co;2-9
Subject(s) - chemistry , selectivity , ketone , allylic rearrangement , ether , trimethylsilyl , stereocenter , medicinal chemistry , alkyl , organic chemistry , catalysis , vinylsilane , lewis acids and bases , enantioselective synthesis
The asymmetric synthesis of enantiomerically pure α ‐substituted tertiary homoallylic ethers 4 a, 11 and 12 a–c by the allylation of ethyl methyl ketone ( 1 a ) with γ ‐substituted allylsilanes 9 a–h is described. The allylsilanes were obtained by a nickel‐catalysed Grignard cross‐coupling reaction of ( E )‐ and ( Z )‐(3‐iodoallyl)trimethylsilane with various Grignard reagents. The reaction of the allylsilanes with 1 a in the presence of the trimethylsilyl ether of N ‐trifluoroacetylnorpseudoephedrine ( 3 ), and catalytic amounts of a mixture of trimethylsilyl triflate and trifluoromethanesulfonic acid led to the homoallylic ethers 4 a, 11 and 12 a–c with two new stereogenic centres, with a selectivity of 1:9 to >20:1 for the homoallylic and of 1:99 to >60:1 for the allylic centre. The facial selectivity does not depend on the configuration of the allylsilane, and in all reactions the anti product is preferentially formed. Interestingly, a pronounced switch of facial selectivity takes place with increasing length of the alkyl group of the allylsilane.