Synthesis of new chiral auxiliares from carbohydrates for Et2AlCl-promoted Diels-Alder reactions

Peptidyl Molecular Imaging Contrast Agents Using a New Solid-Phase Peptide Synthesis Approach

“…The expected transition state is shown in Figure . Previous reports have shown that Et 2 AlCl can bridge two carbonyl groups in a 1,3 position to form a stable 6-membered ring, which leads to bond cleavage adjacent to either carbonyl group ( − ). However, Et 2 AlCl would form an unstable 7-membered ring by bridging the two carbonyl groups of CBZ-Gly-OMe, and this bridge would be further destabilized by the additional planar constraints of the amide and ester groups, so that Et 2 AlCl is more likely to form a strong interaction with just one carbonyl group.…”

Exploiting π shielding interactions of η6 arene chromium (0) complexes: New auxiliaries derived from the biogenic chiral pool

“…Conversion to the acrylate 8 proceeded in moderate yield, allowing us to immediately probe cycloaddition to cyclopentadiene under the influence of various Lewis acids. To aid in determination of facial-and diastereoselectivity, samples of authentic adducts 9 (R = H or alkyl) were also prepared from 10 and 7 [7]. Initial results with alkyl aluminum species were disappointing, though clear preference for endo addition were evident (Table 1, entry 3).…”

“…The solvent was evaporated, and residue dissolved in EtOAc (40 mL) and the solution was washed with water (3 · 100 mL) and brine (1 · 100 mL) then dried over MgSO 4 . The solution was filtered, and the filtrate condensed in vacuo, and the residue was purified by SGC (40:60 EtOAc:hexanes) to give the title compound (968 mg, 97%) as a colorless oil [7]; 5H),5.99 (d,J = 2.1 Hz,1H),4.73 (d,J = 7.2 Hz,1H),4.64 (d,J = 2.4 Hz,1H),4.49 (d,J = 7.2 Hz,1H),1H),4.02 (d,J = 2.1 Hz,1H), 3.97-3.83 (m, 2H), 1.6 (br.s, OH), 1.49 (s, 3H), 1.34 (s, 3H); 13 C NMR (d) 137.3, 128.9, 128.4, 127.9, 112.0, 105.3, 83.0, 82.7, 80.3, 72.1, 61.2, 27.0, 26.5.…”

“…The residue was dissolved in CH 2 Cl 2 (5 mL) and the solution washed with water (3 · 5 mL) and brine (1 · 10 mL), then dried over MgSO 4 , and concentrated in vacuo. The crude residue was purified via SGC (15:85, EtOAc:hexanes) to yield the title compound (40 mg, 74%) as a colorless oil [7]; 1 H NMR (d) 7.34-7.31 (m), 6.41 (dd, J = 17.1 Hz and J = 1.2 Hz, 1H), 6.12 (dd,J = 17.1 Hz,10.5 Hz,1H),5.97 (d,J = 3.6 Hz,1H),5.83 (dd,J = 10.5,1.2 Hz,1H),4.69 (d,J = 12.3 Hz,1H),4.64 (d,J = 3.9 Hz,1H),3H), 3.97 (d, J = 2.7 Hz, 1H), 1.60 (br.s, OH) 1.49 (s, 3H), 1.33 (s, 3H); 13 C NMR (d) 166.1,137.3,131.4,128.8,128.3,128.2,127.9,112.1,105.5,82.3,81.8,78.3,72.1,62.5,27.0,26.5. 4.5. 3-O-benzyl-xylofuranose-2,3-acetonide: arene chromium tricarbonyl complex (11) A 200 mL round bottom flask was charged with 3-Obenzyl-xylofuranose-2,3-acetonide (1.875 g, 6.689 mmol), chromium hexacarbonyl (2.944 g, 13.378 mmol) and a mixture of n-Bu 2 O/THF (96 mL of 6:1 n-Bu 2 O:THF).…”