17417-00-4Relevant articles and documents
Kintya et al.
, (1978)
PROCESS OF PRODUCING ALPHA-HYDROXY COMPOUNDS AND USES THEREOF
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Page/Page column 16-19, (2019/08/29)
New process of producing alpha-hydroxy compounds from sustainable resources useful as platform chemicals, such as hydroxy analogues of amino acids or polymer precursors.
Chiral propargylic cations as intermediates in SN1-type reactions: Substitution pattern, nuclear magnetic resonance studies, and origin of the diastereoselectivity
Nitsch, Dominik,Huber, Stefan M.,Poethig, Alexander,Narayanan, Arjun,Olah, George A.,Prakash, G. K. Surya,Bach, Thorsten
, p. 2851 - 2857 (2014/03/21)
Nine propargylic acetates, bearing a stereogenic center (-C*HXR 2) adjacent to the electrophilic carbon atom, were prepared and subjected to SN1-type substitution reactions with various silyl nucleophiles employing bismuth trifluoromethanesulfonate [Bi(OTf)3] as the Lewis acid. The diastereoselectivity of the reactions was high when the alkyl group R2 was tertiary (tert-butyl), irrespective of the substituent X. Products were formed consistently with a diastereomeric ratio larger than 95:5 in favor of the anti-diastereoisomer. If the alkyl substitutent R2 was secondary, the diastereoselectivity decreased to 80:20. The reaction was shown to proceed stereoconvergently, and the relative product configuration was elucidated. The reaction outcome is explained by invoking a chiral propargylic cation as an intermediate, which is preferentially attacked by the nucleophile from one of its two diastereotopic faces. Density functional theory (DFT) calculations suggest a preferred conformation in which the group R2 is almost perpendicular to the plane defined by the three substituents at the cationic center, with the nucleophile approaching the electrophilic center opposite to R2. Transition states calculated for the reaction of allyltrimethylsilane with two representative cations support this hypothesis. Tertiary propargylic cations with a stereogenic center (-C* HXR2) in the α position were generated by ionization of the respective alcohol precursors with FSO3H in SO2ClF at -80 C. Nuclear magnetic resonance (NMR) spectra were obtained for five cations, and the chemical shifts could be unambiguously assigned. The preferred conformation of the cations as extracted from nuclear Overhauser experiments is in line with the preferred conformation responsible for the reaction of the secondary propargylic cations.
