Stereocontrol in the intramolecular Diels-Alder reaction. 5. Preparation of a tetracyclic intermediate for ikarugamycin

Synthesis of Highly Functionalized Hydrindanes via Sequential Organocatalytic Michael/Mukaiyama Aldol Addition and Telescoped Hydrozirconation/Cross-Coupling as Key Steps: En Route to the AB System of Clifednamides

“…The high diastereoselectivity of the IMDA reaction presumably originates from the stereochemical substitution of linear precursor 9 , which would favor the transition state toward 8b over 8b ′. This assumption is in good agreement with the transition-state geometries proposed by Boeckman and our previous DFT calculations for the IMDA reaction of the comparably substituted linear precursor 7 to the trans -hydrindane 8a . The calculations revealed a favored transition state toward 8a with the same stereochemical pattern as 8b .…”

2-(Phenylsulfonyl)-1,3-dienes as versatile synthons in organic transformations. Multicoupling reagents and Diels-Alder dienes with a dual electron demand

“…NMR 7.85-7.45 (m, 10 H, ArH), 6.81 (m, 1 H, vinylic H), 5.54 (dq, J = 15.9, 1. 4 Hz, 1 H, MeCH=CH), 5.32 (dq, J = 15.9, 6.3 Hz, 1 H, MeC//=CH), 3.31 (m, 1 H, HC-Me), 2.18 (unresolved m, 2 H, allylic ), 1.92 (br t, 2 H, homoallylic ), 1.63 (dd, J = 6.3, 1.4 Hz, 3 H, HC=CHCH3), 1.42 (d, J = 7.35 Hz, 3 H, HCCH3); 13C NMR 141.50, 138.69, 137.41, 134.77, 133.78, 133.25, 130.56, 129.04, 128.34, 127.81, 121.90, 67.90, 33.74, 25.43, 20.46, 18.47, 16.77. cyclohexene (4).…”

“…This result is probably due to formation of an anion of the malonate, which directs copper and hence the cuprate addition to the «-position. Reaction of 4 with lithium dimethylcuprate gave cis-1,4-dimethyl-2-cyclohexene as expected from an anti substitution of the phenylsulfonyl group in the trans isomer 4 (entry l).12 The stereochemistry of the product was unambiguously established by NMR.13…”

Stereoselective synthesis of cis-decalins via Diels–Alder and double Michael addition of substituted Nazarov reagents

“…For example, when tosylate 39, prepared in four steps from the cycloaddition of Nazarov reagent l l b (Scheme 6), was treated with potassium tert-butoxide in a mixture of tetrahydrofuran-tert-butanol, an 86% yield of the known tricyclic compound 40 was isolated (15). However, the corresponding higher homolog 35 obtained from l l c via 33 gave none of the tricyclic adducts 36.…”

“…The combined organic layers were washed with brine (1 X 10 mL), dried, filtered and the solvents were removed under reduced pressure. The residue was purified by flash chromatography with hexane -ethyl acetate (3: 1) to afford substituted Nazarov reagent l l a (22 rng, 35%); ir (cm-I): 1725, 1690, 1670, 1630, 1600, 1150; 'H nmr (6) 3-Brorrzo-I-fefr-nhydr-opyrnttyloqi-prone (15) To a solution of 3-brornopropanol (10.0 g, 0.072 rnol) in 500 mL of anhydrous THF at O°C were added 7.84 g of dihydropyran (0.093 rnol) and 1.3 g of p-toluenesulfonic acid (0.007 rnol). The resulting mixture was stirred at O°C for 1 h and at room temperature for 12 h, then it was poured into 750 mL of saturated sodium bicarbonate.…”