First green protocols for the large-scale preparation of γ-diisoeugenol and related dihydro(1H)indenes via formal [3+2] cycloaddition reactions

Trans-isoeugenol and related styrenes (trans-isohomogenol or C-benzylated isoeugenol), important components of the essential oil of various tropical plants, dimerize easily in the presence of catalytic amounts of BF(3)center dot OEt(2) in poly(ethylene glycol) with M(n) = 400 (PEG-400) or SiO(2)-OSO(3)H in MeCN via formal [3+2] cycloaddition reaction to give respective natural products (diisoeugenol and its O-substituted analog) with the 1,2-trans-2,3-trans-configuration in excellent yields. gamma-Diisoeugenol scale-up preparation has also been described. (C) 2009 Elsevier Ltd. All rights reserved.