Allylation of active methylene compounds with cyclic Baylis–Hillman alcohols: a DFT study

Abstract

International audienceAllylation reaction of active methylene compounds with cyclic Baylis–Hillman (BH) alcohol catalyzed by 4-dimethyamino-pyridine (DMAP) has been investigated by means of density functional theory with B3LYP/6-311++G(d,p). The first step on the chemical path is considered as an acid–base reaction. It is then followed by allylation of active methylene compound with cyclic BH alcohol. Calculated gas-phase pKa values illustrate that active methylene compounds have higher acidity than the considered cyclic BH alcohol. The DMAP catalytic activity may be interpreted as a proton transfer bridge between the active methylene compounds and the cyclic BH alcohol. Two alternative competing reactivity sites are present. Regioselectivity has been carried out on the base of natural atomic charge, Fukui index. The computations help rationalizing the fact that the direct allylation is the favored reaction and leads to the end-product

Metal catalyst-free N-allylation/alkylation of imidazole and benzimidazole with Morita–Baylis–Hillman (MBH) alcohols and acetates

“…Mechanistically, we believe that the nucleophilic allylic substitutions of alcohols 4 , such as 4a , starts with a conjugate addition of imidazole ( 2a ) at the C-β position of the Michael acceptor 4a , followed by elimination of the hydroxy moiety, affording the intermediate I . Similarly, a further second β’-conjugate addition of imidazole ( 2a ) to I might occur, followed by elimination of imidazole ( 2a ) finally providing the allylated derivative 6a ( Scheme 2 ) [ 24 – 26 31 ]. It is notable, that such reaction mechanism involving the intermediate I was previously explored by Smith [ 32 ] and supported by studies of Tamura [ 33 ].…”

“…In our first experiment, this substrate did not react with imidazole (2a) in toluene at reflux within 24 h, with or without azeotropic distillation, and the starting materials were completely recovered (Table 2, entry 1). Moreover, the addition of additives to the previous reaction mixture, such as DMAP [24][25][26]31] or molecular sieves 4 Å, commonly used to mediate nucleophilic allylic substitutions, did not lead to a notable improvement of the reaction outcome (Table 2, entries 2 and 3). However, the use of DABCO, commonly used as a powerful catalyst or a nucleophilic additive in the reaction of acyclic MBH adducts with various nucleophiles [21,[34][35][36][37], did not afford the S N 2/S N 2' products but provided the 1,4-adduct 8a in 84% yield (Table 2, entry 4).…”

Mechanistic study on silver(I)-catalyzed aminofluorination of unactivated alkenes

“…At present, owing to the lack of effective means to directly capture the Ag(II) and Ag(III) intermediates in the reaction solution, the study on the mechanism for this reaction is still a difficult problem. Luckily, quantum chemical calculation, particularly the density functional theory, is well suited for the mechanistic study . With the continuing interest in the silver‐catalyzed radical reactions, in the present work, a systematic study will be conducted on the mechanism for the Ag(I)/Selectfluor‐catalyzed aminofluorination of unactivated alkenes with density functional theory, including the rate‐determining step and regioselectivity.…”