Stereochemistry of protonation at carbon of nitronate adducts from 1,6-conjugate addition of Grignard reagents to 9-nitroanthracenes. Crystal structure of cis-9-benzyl-10-nitro-9,10-dihydroanthracene
- 1 January 1982
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 8,p. 929-932
- https://doi.org/10.1039/p29820000929
Abstract
Addition of RMgX (a, R = CH3; b, R = PhCH2) to 9-nitroanthracene (4) leads to formation of 1,6-adduct (5) in high yield. On treatment with dilute acetic acid, (5) is converted into the corresponding 10-alkyl-9,10-dihydroanthracene-9-nitronate anion (7), which quickly undergoes a stereoselective protonation at C-9 to give almost exclusively cis-10-alkyl-9-nitro-9,10-dihydroanthracene (8). Both (8a and b) remain unaltered under isomerization conditions. The formation of the more stable isomer, under kinetic control conditions, in a true boat system as (6), is interpreted in terms of a steric control on the proton approach, exerted by the axial alkyl group in position 10. The structure assignment of (8a, b) has been made by X-ray analysis of the benzyl derivative (8b). Structural parameters are discussed in comparison with those reported in the literature for analogous systems.Keywords
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