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[4 + 2]-Cycloaddition and 1,4-Addition of ortho-Quinone Methides by a Chiral Crotyl Silane
- Wong, Christopher R., Hummel, Gerald, Cai, Yongqi, Schaus, Scott E., Panek, James S.
- Organic letters 2018 v.21 no.1 pp. 32-35
- carbon, chemical reactions, chemical structure, enantioselectivity, ferric chloride, quinones, silanes
- Anhydrous FeCl₃ in the presence of 2,6-lutidine promotes the substrate-controlled enantioselective [4 + 2]-cycloaddition and crotylation reaction between an enantioenriched (S,E)-crotyl silane and in situ generated ortho-quinone methides (oQMs). The reaction produces both the chiral chroman and crotylation products in a ratio reflective of the electronic nature of the parent oQM with overall combined yields up to 96%. A ring-opening and elimination sequence was subsequently developed to provide direct access to the crotylation products, containing two contiguous tertiary carbon stereocenters, in good yields and enantioselectivities.