Abstract
The treatment of 2-(2-vinylphenyl)acetaldehydes or 3-(2-vinylphenyl)propanals with BF3·Et2O results in an intramolecular Prins reaction affording intermediary benzyl carbenium ions, which are then trapped by a variety of electron-rich aromatics via Friedel–Crafts alkylation. This cascade Prins/Friedel–Crafts cyclization protocol paves an expedient path to medicinally useful 4-aryltetralin-2-ol and 5-aryltetrahydro-5H-benzo[7]annulen-7-ol derivatives.
Highlights
4-substitituted tetralin-2-ols and derivatives with significant pharmaceutical activities have been identified, only a limited number of synthetic methods is documented in the literature (Scheme 1) [7,8,9]
Our research began with the preparation of 2-(2-vinylphenyl)acetaldehydes (13) required as substrates for the Prins/ Friedel–Crafts cyclization reactions
Ic alkenyl aldehydes were previously prepared via a three step process as exemplified by 13a shown in Scheme 3 consisting of the following steps: (i) Wittig reaction of 2-bromobenzaldehyde with methyltriphenylphosphonium iodide ylide, (ii) lithiation of the resultant o-bromostyrene with n-BuLi and reaction of the aryl lithium species with ethylene oxide, and (iii) oxida
Summary
4-substitituted tetralin-2-ols and derivatives with significant pharmaceutical activities have been identified, only a limited number of synthetic methods is documented in the literature (Scheme 1) [7,8,9]. The intermediate 6 would undergo a Prins-type intramolecular cyclization with the olefinic bond to produce a stable benzyl carbocation 7, that may be trapped through a Friedel–Crafts alkylation with an aromatic substrate or through the reaction with an external nucleophile to afford the target product 8.
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