Premium
Tetrabutylammonium Decatungstate‐Photosensitized Alkylation of Electrophilic Alkenes: Convenient Functionalization of Aliphatic CH Bonds
Author(s) -
Dondi Daniele,
Fagi Maurizio,
Albini Angelo
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200501216
Subject(s) - chemistry , alkylation , electrophile , radical , photochemistry , alkene , nucleophile , hydrogen atom abstraction , photoredox catalysis , adduct , medicinal chemistry , catalysis , organic chemistry , photocatalysis
Tetrabutylammonium decatungstate (TBADT, 2×10 −3 m ) is an effective photocatalyst for the alkylation of electrophilic alkenes (0.1 m , α,β‐unsaturated nitriles, esters, ketones) by alkanes, alcohols, and ethers. The products are in most cases obtained in >70 % isolated yields, through an experimentally very simple procedure. The kinetics of the radical processes following initial hydrogen abstraction by excited TBADT in deoxygenated MeCN have been studied. In the absence of a trap, back hydrogen transfer from reduced tungstate is the main pathway for alkyl radicals, while α‐hydroxyalkyl radicals are oxidized to ketones by ground‐state TBADT. With both radical types the reaction ceases at a few percent conversion. However, trapping by electrophilic alkenes is followed by reduction of the radical adduct and regeneration of the catalyst, which allows the alkylation to proceed up to complete alkene conversion with the mentioned good yields of products. With a nucleophilic (α‐hydroxyalkyl) radical, alkylation is efficient ( Φ = 0.58) and can also be carried out when degassing is omitted, the only difference being a short induction period. With a less reactive (cyclohexyl) radical, the quantum yield is lower ( Φ = 0.06) and the reaction is considerably slowed in aerated solutions, but the chemical yield remains good.