128495-75-0Relevant academic research and scientific papers
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.
Nucleophilic addition of organometallic reagents to N,N-dimethyl- and SAMP-glyoxal-monohydrazones
Cere, Vanda,Peri, Francesca,Pollicino, Salvatore,Ricci, Alfredo
, p. 1087 - 1098 (2007/10/03)
Nucleophilic addition of organometallics to N,N-dimethyl-glyoxal- monohydrazone occurs smoothly to give the corresponding α-hydroxy hydrazones in high yields. From these compounds, polyfunctional derivatives such as protected α-hydroxy aldehydes and α-hydroxy nitriles can be easily obtained in satisfactory to good yields. The addition to a SAMP-hydrazone proceeds with low (35% d.e.) or reasonable (60% d.e.) levels of stereoselectivity when vinylmagnesium reagents are employed.
Diastereoselectivity of the conjugate addition of organocopper reagents to γ-alkoxy α,β-unsaturated carbonyl derivatives. Importance of the reagent type and the double-bond geometry
Yamamoto, Yoshinori,Chounan, Yukiyasu,Nishii, Shinji,Ibuka, Toshiro,Kitahara, Haruo
, p. 7652 - 7660 (2007/10/02)
Systematic investigations of the diastereoselectivity of organocopper conjugate addition to γ-alkoxy trans enoates (3), cis enoates (4), and diesters (5) revealed that the selectivity highly depended on the substrate structure and the reagent type. The an
Asymmetric Hetero-Diels-Alder Reaction of α-Alkoxy Aldehydes with Activated Dienes. The Scope of Lewis Acid Chelation-Controlled Cycloadditions
Midland, M. Mark,Koops, Roger W.
, p. 5058 - 5065 (2007/10/02)
The cycloaddition reactions of various α-alkoxy aldehydes with 1,3-dimethoxy-1--1,3-butadiene (Brassard's diene, 2) were performed under the Lewis acid catalysis of Eu(hfc)3, magnesium dibromide, or diethylaluminum chloride.Moderate to high diastereoselectivities were observed with Eu(hfc)3 and magnesium dibromide.Evidence from reactions of Eu(hfc)3 and magnesium dibromide catalysis indicated a possible "chelation-control" pathway.Lewis acid catalysis from diethylaluminum chloride provides products with moderate to high diastereoselectivity.The mechanistic pathway with catalysis by diethylaluminum chloride was less clear.A possible mechanism based upon a "Cram" addition is considered.
