Reduction of Unsaturated 1,4-Diketones by Aluminum Isopropoxide¹

Nucleophilic attack on a carbonyl group conjugated to a chiral centre: a search for a vinylogous Cram's rule

“…We find that the diols (7) and (8) are produced in the disappointingly low ratio of ca. Later work * assigned the meso configuration (7) to this diol.…”

“…The (E)-1,4-Diphenylbut-2-ene-1,4-diols (7) and @).-The separated diphenylbutyne-174-diols (1 mmol) were each refluxed in ether (15 ml) with lithium aluminium hydride (2 mmol) for 1 h. Work-up using aqueous sodium potassium tartrate gave the appropriate diol and 1,4-diphenylbutadiene, which were separated by fractional crystallisation from ether for compound (7) and by chromatography (SiO,, ether-pentane) for compound (8): (RS,SR)-isomer (7) 9). -2-Phenyl-3styryloxirane'2 (135 mg) was kept at room temperature in methanol (6 ml) with toluene-p-sulphonic acid (1 mg) for 1 day after which time ether was added.…”

Stable carbocations. CLXXXVI. Relation of carbon-13 NMR shifts to the effect of methyl substitution on electronic charge distribution at trigonal carbons

“…The 13C chemical shift is a property which is known to be related to charge densities, but the best correlations with charges have been observed for trigonally hybridized carbons where the differences in total charges are controlled primarily by differences in -charge densities, i.e., in situations such as the para carbons of monosubstituted ben-zenes29 and the carbons in monocyclic aromatic ring systems. 30 For these systems, even the most simple -approximation MO methods successfully reproduce the shielding trends. Several approaches have been devised for the theoretical estimation of l3C chemical shifts, and most of these are based on charge densities, as well as other calculated or assumed quantities such as excitation energies and bond orders.…”

“…These contributions to the -methyl SCS cannot be discounted, although the use of the Karplus-Pople theory has sometimes given less satisfactory results than correlations with charge calculations alone. Another postulated factor is a neighboring-group diamagnetic shielding of about 30 ppm produced by replacement of carbon for hydrogen in methyl substitution. 41 If this shielding factor is included, it is obvious that the deshielding influences on C" must be substantial to result in the overall downfield shift caused by methyl substitution.…”

HYDRIDE REDUCTIONS OF THE CIS AND TRANS-DIBENZOYLSTILBENES1

“…This investigation, initiated under supporting fellowships,2• 3 was completed under a research grant from the Office of Ordnance Research.2 du Pont Company Postgraduate Fellow,[1949][1950] (see ref.1).3 Supported in part by a grant from the Office of Ordnance Research 4. Tennessee Eastman Corporation Graduate Scholarship, 1948-1949, under which the preliminary work was done on the reduction of the dimethyldibenzoylethylenes (see ref.2).…”