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Efficient Synthesis of All-Carbon Quaternary Centers via the Conjugate Addition of Functionalized Monoorganozinc Bromides
Published on: May 26, 2019
All-Carbon Quaternary Center Containing Tetrahydro-5H-benzo[c]fluorenes via Highly Stereoselective Transannular
Kasam Poonswat1, Sineenart Attanonchai2, Paratchata Batsomboon2
1Program in Chemical Sciences, Chulabhorn Graduate Institute, 54 Kamphaeng Phet 6 Road, Laksi, Bangkok, 10210, Thailand.
Abstract:
Transannular carbocation cyclization of the achiral benzannulated cyclononene tertiary alcohols under acid catalysis furnished the [5/6]-fused tetracycles with three contiguous stereogenic centers, one of which is an all-carbon C11b quaternary center, in good-to-excellent yields and diastereoselectivity. Hydride, water, azide, allyl, and electron-rich (hetero)arenes could be employed as nucleophiles. The reaction is under both substrate- and condition-control. Further, functionalization of some selected substrates was also demonstrated. Computational chemistry delineated different competing reaction pathways such as direct substitution at the bisbenzylic position for other related systems-the benzannulated cyclooctene/cyclononene secondary alcohols and provided further evidence for the observed stereoselectivity.
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Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

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