No abstract

We developed an efficient fluorination protocol that converts easily accessible aziridines into β-fluoroamines, which are important motifs in biologically active molecules. In contrast with traditional fluorination approaches, DMPU-HF has shown both higher reactivity and regioselectivity and good functional group tolerance; thus, a wide scope of β-fluoroamines can now be accessed conveniently. The stereochemical behavior of ring opening depends on the substitution pattern of the aziridine substrates.

The experimental and theoretical behavior of the (OC)CCH 3JCH coupling constant is investigated for a series of α,β‐unsaturated compounds (1 to 8), and for some of them, the well‐known relationship (3JCHcis < 3JCHtrans) was observed. However, for some compounds, close values for 3JCHcis and 3JCHtrans couplings were observed, and for aldehydes group containing compounds (7 and 8E), an inversion order is observed (3JCHcis > 3JCHtrans). In all cases where the 3JCHcis < 3JCHtrans relationship it is not followed, a polar group or electronegative atom oriented in opposite direction (s‐trans) to the HCC hydrogen is present, suggesting that conformational preference of such polar group or atoms are important factor on the behavior of 3JCH couplings. Taking all of these in consideration, a new Karplus‐type equation was proposed for 3JCH couplings in α,β‐unsaturated compounds, which can be used for configurational and conformational assignment on trisubstituted double bond derivatives.

Long-range proton-fluorine coupling constants ( n J HF ) are helpful for the structure elucidation of fluorinated molecules. However, their magnitude and sign can change with the relative position of coupled nuclei and the presence of substituents. Here, trans-4-tert-butyl-2-fluorocyclohexanone was used as a model compound for the study of the transmission of 4 J HF . In this compound, the 4 J H6axF was measured to be +5.1 Hz, which is five times larger than the remaining 4 J HF in the same molecule ( 4 J H4F = +1.0 Hz and 4 J H6eqF = +1.0 Hz). Through a combination of experimental data, natural bond orbital (NBO) and natural J-coupling (NJC) analyses, we observed that stereoelectronic interactions involving the π system of the carbonyl group are involved in the transmission pathway for the 4 J H6axF . Interactions containing the π system as an electron acceptor (e.g., σ C6 H6ax ! π * C═O and σ C F ! π * C═O ) increase the value of the 4 J H6axF , while the interaction of the π system as an electron donor (e.g., π C═O ! σ * C F ) decreases it. Additionally, the carbonyl group was shown not to be part of the transmission pathway of the diequatorial 4 J H6eqF coupling in cis-4-tert-butyl-2-fluorocyclohexanone, revealing that there is a crucial symmetry requirement that must be fulfilled for the π system to influence the value of the 4 J HF in these systems.