Stereoselective titanium-mediated aldol reactions of α-benzyloxy methyl ketones

Cobalt-Catalyzed Oxygenation/Dearomatization of Furans

“…Purification by flash chromatography (50:50 hexane/EtOAc) afforded alcohol 9a as a colorless oil (0.001 g, 10%). The spectroscopic data are consistent with the data reported: 21 1 H NMR (600 MHz, CDCl 3 ) δ 4.50 (m, 1H), 4.27 (m, 1H), 2.87 (dd, J = 17.9, 6.5, 1H), 2.53 (dd, J = 17.9, 3.8, 1H), 2.00 (d, J = 4.2, 1H), 1.39 (d, J = 6.6, 3H); 13 C NMR (150 MHz, CDCl 3 ) δ 174.7, 83.9, 73.3, 37.6, 18.8.…”

“…The peroxidation of disubstituted furans was diastereoselective, forming the resulting lactones as single diastereomers (entries 4–7). The relative configuration of the disubstituted lactones was found to be trans , which was determined by converting silyl peroxide 9 to known alcohol 9a (Scheme ) and comparing the 1 H and 13 C NMR chemical shifts to reported values . Isolating only one diastereomer of the product was not expected because the cobalt-catalyzed oxygenation of alkenes is typically not diastereoselective. − Selectivity has been observed only in systems in which the diastereotopic faces of the alkenes are sterically quite distinct. − …”

Phyllospongianes A–E, Dinorscalarane Sesterterpenes from the Marine SpongePhyllospongia foliascens

“…COSY correlations of H 2 -2′ (δ H 2.34)/H 2 -3′ (δ H 3.67), H 2 -3′/H-4′ (δ H 1.67), H-4′/H 3 -5′ (δ H 0.93), and H-4′/H 3 -6′ (δ H 0.90) and HMBC correlations from H 2 -2′ and H-12 (δ H 5.45) to C-1′ (δ C 172.3), along the molecular formula, confirmed the hydroxy substitution at C-3′ (δ C 72.8) in 3 (Figure ). The absolute configuration of C-3′ was determined to be R by comparison of the specific rotations of ( R )-3-hydroxy-4-methylpentanoic acid ([α] D +39.8, CHCl 3 , c 1.0) with ( S )-3-hydroxy-4-methylpentanoic acid ([α] D −25.3, CHCl 3 , c 1.2) − and those of 3 ([α] D 25 +62.7, MeCN, c 0.1) with 2 ([α] D 25 +40.7, MeCN, c 0.1), respectively. Additionally, the specific rotation of the 3-hydroxy-4-methylpentanoic acid subunit in 3 ([α] D 25 +2.1, CHCl 3 , c 0.1) (differences in measured versus literature values likely stem from inaccuracies in the weight of this hydrolysis fragment), determined after hydrolysis and purification by mini-chromatographic column on silica gel (200 mesh, CH 2 Cl 2 /MeOH, 20:1), confirmed the R -configuration for C-3′.…”