Inter‐ and Intramolecular Hetero Diels‐Alder Reactions, 36. Synthesis of Dihydropyrans by Hetero Diels‐Alder Reaction of Enaminones An Efficient Route to 3‐Amino Sugar Derivatives

A stereoselective synthesis of 6,6,6-trifluoro-l-daunosamine and 6,6,6-trifluoro-l-acosamine

“…Filtration and concentration under reduced pressure gave a colourless oil. Purification by column chromatography (10% ethyl acetate-hexanes) gave the title compound 16 (565 mg, 84%) as a white solid; mp 144 5.32 (1H, q, J 6.8 Hz, CH(Ph)CH 3 ), 7.37-7.43 (5H, m, Ph); 13 C NMR (75 MHz, CDCl 3 ) d 14.9, 17.5, 32.7 (C-2), 55.9, 58.1, 62.6, 64.7, 75.2 (q, J 29 Hz, C-5), 100.1 (C-1), 116.6 (q, J 288 Hz, CF 3 ), 123.7 (q, J 281 Hz, CF 3 ), 128. The structure was solved using SHELXS 9 and refined by full-matrix least-squares using SHELXL-97 10 and TITAN2000.…”

“…Tietze et al 5 have reported a hetero-Diels-Alder approach to racemic 3-amino-carbohydrate derivatives and we have previously described the syntheses of 2,6-dideoxy-6,6,6-trifluoro-D-and Larabino-hexose using the Diels-Alder reaction of hetero-diene 8 and ethyl vinyl ether. 6, 7 We now report on a short and efficient synthesis of 6,6,6-trifluoro-L-acosamine and 6,6,6-trifluoro-Ldaunosamine derivatives using an adaptation of this method.…”

Synthesis of 3,4-dihydro-2H-pyrans by hetero-Diels–Alder reactions of functionalized α,β-unsaturated carbonyl compounds with N-vinyl-2-oxazolidinone

“…(408 mg, 59%) colourless crystals, mp 179 • C (ethanol); (Found: C, 72.9; H, 5.2; N, 8.2. C 21 H 18 N 2 O 3 requires C, 72.8; H, 5.2; N, 8.1%); m max (KBr disk)/cm −1 3027, 2923, 2962, 2883 (CH), 2200 (CN), 1767 (CO), 1611 (C=C); d H (500 MHz; CDCl 3 ; Me 4 Si) 2.10 (1H, dt, J 11.8, 13.5, 3-H ax ), 2.41 (1H, ddd, J 1.5, 6.3, 13.5, 3-H eq ), 3.58 (1H, dt J 8.8, 5.3, 4 B-H), 3.74 (1H, q, J 8.5, 4 A-H), 4.01 (1H, dd, J 11.8, 6.3, 4-H), 4.39 (1H, q, J 8.5, 5 B-H), 4.42 (1H, ddd, J 8.8, 8.5, 5.5, 5 A-H), 5.93 (1H, dd, J 11.5, 1.5, 2-H) and 7.33 (23), 278 (9), 261 (9), 113 (100), 105 (64) and 77 (35). q, J 12.5, 3-H ax ), 2.42 (1H, ddd, J 2.0, 6.5, 13.5, 3-H eq ), 3.60 (1H, dt J 8.3, 5.5, 4 B-H), 3.74 (1H, q, J 8.0, 4 A-H), 4.11 (1H, dd, J 11.5, 6.5, 4-H), 4.39 (1H, q, J 8.…”

“…Hetero-Diels-Alder reactions of a,b-unsaturated carbonyl compounds containing a 1-oxa-1,3-butadiene system with electronrich olefins lead to 3,4-dihydro-2H-pyran derivatives which are valuable precursors for the synthesis of many natural products such as carbohydrates, alkaloids and antibiotics. [1][2][3][4][5][6][7][8][9][10] These reactions have been classified as cycloadditions with inverse electron demand. 11 The reactivity of a,b-unsaturated carbonyl compounds in hetero-Diels-Alder reactions is generally low and the reactions require high temperature 12-13 or high pressure.…”

Regioselective Synthesis of Rare 3-Halomethylphenols Based on Formal [3+3] Cyclizations of 1,3-Bis(trimethylsilyloxy)-1,3-butadienes

“…The reaction of difluorochloroacetic anhydride (2a) with ethylvinyl ether (1a) afforded the known 22 enone 3a (Scheme 1, Table 1). The reaction of acid chlorides 2b-d with enol ethers 1a,b gave the difluorobromomethyl-, dichloromethyl-, and trichloromethyl-substituted enones 3b-e.…”