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Asymmetric Induction in the Wittig‐Still Rearrangement of Ethers Containing an Allylic Stereocenter – Diastereocontrol by Allylic Oxygen
Author(s) -
Priepke Henning,
Brückner Reinhard
Publication year - 1990
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19901230128
Subject(s) - allylic rearrangement , chemistry , stereocenter , stereochemistry , alkoxy group , asymmetric induction , epimer , chirality (physics) , selectivity , medicinal chemistry , enantioselective synthesis , organic chemistry , alkyl , catalysis , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark
Stannylated allyl ethers 13, 15, 19 , and 21 bearing an allylic center of chirality are submitted to the Still variant of the [2,3] Wittig rearrangement. In these reactions alkoxy groups at the chiral center exert stereocontrol through asymmetric induction. With only few exceptions, the syn‐configurated rearrangement product ( 27 ) is formed in preference to the anti epimer ( 28 ). syn: anti ratios are often > 90 : <10 and repeatedly ≥98: ≤2 ( 27/28f,g,m,n ). The dependence of asymmetric induction from the structure of the starting material is investigated. The formation of syn product is particularly favorable in unhindered substrates (Scheme 4 ) with Z rather than E configuration (Table 5). Allylic MOMO and MEMO groups induce higher syn:anti ratios than allylic alkoxy groups (Scheme 5). Anionic allylic directing groups effect modest levels of anti selectivity (Scheme 6). Cyclic n‐membered ethers can rearrange with more ( n = 5) or less ( n = 6) syn selectivity than open‐chain analogs (Scheme 7 ). – The magnitude of the vicinal coupling constant 3 J between β‐ and γ‐protons may be used to assign the stereochemistry in epimeric syn and anti γ‐alkoxy alcohols.