Deformative Transition of the Menschutkin Reaction and Helical Atropisomers in a Congested Polyheterocyclic System

Abstract

A 4,7-phenanthroline polycyclic 1A designed for probing the limits of the Menschutkin reaction was synthesized in a six-step sequence. The rotational barrier of the phenyl ring nearby the N-methyl group in rac-2A was estimated to be ≫ 18.1 kcal/mol from VT-NMR experiments, making them a new type of helical atropisomer. The methylation rate constants of 9 and 1A with MeI was found to be 2.22 × 10(-4) and 9.62 × 10(-6) s(-1) mol(-1) L, respectively; thus, the formation rate of (P/M)-2A is one of the slowest rates ever reported for a Menschutkin reaction. The N-methyl protons in (P/M)-2A exhibit a significant upfield shift (Δδ 1.0 ppm) in its (1)H NMR, compared to those without a nearby phenyl, indicating a strong CH-π interaction is involved. Conformational flexibility in dipyridylethene 9 is clearly shown by its complexation with BH3 to form helical atropisomers (P,P/M,M)-10. The pKa values of the conjugate acids of 1A and 9 in acetonitrile were determined to be 4.65 and 5.07, respectively, which are much smaller compared to that of pyridine 14a (pKa = 12.33), implying that the basicity, nucleophilicity, and amine alkylation rates of 1A and 9 are markedly decreased by the severe steric hindrance of the flanking phenyl rings in the polyheterocycles.

Fully Synthetic Approach toward Transition Metal–Nitrogen–Carbon Oxygen Reduction Electrocatalysts

“…Synthesis of the pyridinic arene and complexation was performed based on the literature , and is depicted in Scheme . Compound 6 described in Scheme is termed PyrN-Ar for simplicity in this article.…”

Stereochemical Investigation of the Products of the Photoinduced Perfluoroalkylation–Dimerization of Anthracene

“…Thus, this isomer has hitherto unknown atropisomeric chirality with the axis along the linking C-9–C-9′ bond of the two 9,10-dihydroanthracene rings. Two enantiomers were assigned as S (left in Figure ) and R (right) on the basis of the Cahn–Ingold–Prelog rules. , Thus, viewing the structure along the chiral C-9–C-9′ axis and applying the same rule for axially chiral compounds of the preference of closer groups rather than farther ones, the front CF 3 group (shown in red in Figure c) should be the highest priority and the hydrogen atom on the front (blue) next. Then the absolute configuration of the isomer on the left side of Figure was assigned as Sa and the right as Ra .…”