147394-32-9Relevant academic research and scientific papers
Photoinduced Molecular Transformations. Part 137. New General Synthesis of 3-Substituted 3,4-Dihydro-1H-benzopyran-1-ones (3,4-Dihydroisocoumarins) via Radical and Photochemical Fragmentations as the Key Step
Kobayashi, Kazuhiro,Konishi, Atsushi,Kanno, Yoshikazu,Suginome, Hiroshi
, p. 111 - 116 (2007/10/02)
A new general method for a two-step synthesis of 3-substituted 3,4-dihydro-1H-benzopyran-1-ones (3,4-dihydroisocoumarins) is described.This method involves either regioselective alkoxyl radical fragmentation or regioselective photochemical fragmentation as the key step. 2-Hydroxyalkylation of a lithiated o-tolyl tert-butyl ketone with aromatic and aliphatic aldehydes and ketones gave equilibrated mixtures of 1-tert-butyl-3,4-dihydro-1-hydroxy-3-alkyl (or 3-aryl)-1H-2-benzopyrans and their ring-opened isomers in 42-94percent yield.Photolysis of mixtures in chloroform withPyrex-filtered light gave 3-alkyl (or 3-aryl)-3,4-dihydro-1H-benzopyran-1-ones (3,4-dihydroisocoumarins) in 27-64percent yield as exclusive isolable products.On the other hand, photolysis of hypoiodites of the equilibrated mixture in benzene containing mercury(II) oxide and iodine gave the 3-substituted dihydroisocoumarins in 37-64 percent yield with an accompanying formation of phthalide, arising from a radical cascade process triggered by β-scission of the alkoxyl radicals generated from the ring-opened isomer of the lactones.The formation mechanisms of all the products are discussed.
