Reduction of 2-Alkyl-2-carbomethoxy-cyclopentanone Derivatives with Sodium Borohydride. II. The Elucidation of the Diastereoselective Control^a

Synthesis and reactions of a new 1,1-disubstituted cyclopentadiene.

“…triflate to give the corresponding silylated enol ether 2, which was directly oxidized by bubbling oxygen through a vigorously stirred DMSO solution in the presence of Pd(OAc) 2 as the catalyst to give the known 4 enone 3 in 82% yield of chromatographed product. NaBH 4 reduction of 3 in the presence of CeCl 3 ·7H 2 O following the Luche procedure, 3,5 gave the known 4 allylic alcohol 4, which was subjected as such to acid catalyzed dehydration to give cyclopentadiene 5 in 66% yield of chromatographed product (Scheme 1).…”

“…Crystallization of the above product from toluene / pentane 5:6 (1.1 mL), provided the analytical sample of 7 as white solid (146 mg, 45%), mp 145-146 ºC. R f = 0.87 (silica gel, 10 cm, CH 2 Methyl (1R,4S,5S,6R,7s)-7-benzyl-5,6-bis(phenylsulfonyl)bicyclo[2.2.1]hept-2-ene-7-carboxylate (8). A solution of crude diene 5 (296 mg, 1.38 mmol) and cis-1,2-bis(phenylsulfonyl)ethylene (468 mg, 1.52 mmols) in anhydrous toluene (5 mL) was heated to 100 ºC for 15 h. The solution was allowed to cool to room temperature and concentrated in vacuo to give a brown viscous oil that was subjected to column chromatography (silica gel, 35-70 µm, 50 g, hexane / EtOAc mixtures).…”

“…The dried organic phase (anhydrous Na 2 SO 4 ) was concentrated in vacuo to give methyl 1-benzyl-2-(trimethylsilyloxy)ciclopent-2-enecarboxylate 2 (750 mg) as yellow oil, that was used as such in the next step. R f = 0.41 (silica gel, 10 cm, hexane / EtOAc 7:3 2 (30 mg, 0.13 mmol) was added and the red-brown mixture was vigorously stirred for 24 h while oxygen was being bubbled through the mixture via a syringe. The mixture was diluted with EtOAc (10 mL) and was washed with water (8 mL).…”

Stereoselective Synthesis of Bicyclo[4.2.1]nonanes – a Temporary‐Bridge Approach to Cyclooctanoids

“…The treatment of 3a with LiAlH 4 yielded an inseparable 4:1 mixture of 5a epimers (wherein the major epimer was β‐OH), while the partial reduction of 3b with NaBH 4 in methanol yielded a separable 4:1 mixture of 5b epimers (wherein the major epimer was α‐OH, see Table 2). 20…”

γ-Lactone Synthesis via Palladium(II)-Catalyzed Lactonization of Unactivated Methylene C(sp3)–H Bonds

“…The formed suspension was filtered, the filtrate concentrated at reduced pressure and the products isolated by flash chromatography. 3…”