Claisen rearrangement of N-allylketene O, N-acetals

Application of the Novel Tandem Process Diels-Alder Reaction/Ireland-Claisen Rearrangement to the Synthesis of rac-Juvabione and rac-Epijuvabione

“…Thus, an average yield of 85% for each of the three steps was achieved. The individual diastereoisomers were characterized by comparison of their 1 H-and 13 C-NMR spectra with the data obtained for the corresponding esters [21] and their structure confirmed by iodolactonization (Scheme 5) [25]. Thus, treatment of a hydrogen carbonate solution of the mixture 5 in MeCN with I 2 gave the iodolactone mixture in 71% yield, from which the major diastereoisomer 6 was isolated in 40% yield after flash chromatography.…”

“…13 C-NMR (100 MHz, CDCl 3 ): major (48%) (AE)-rel-(bR,1R,4S)-7: 179.6 (COOH); 174.5 (COOMe); 132.8 (C(2)); 125.2 (C(3)); 51.8 (COOMe); 40.0 (C(4)); 39.3 (C(1)); 38.6 (C(a)); 33.9 (C(b)); 23.9 (C(5)); 21.4 (C(6)); 16.2 (MeÀC(b)); minor (32%) (AE)-rel-(bR,1R,4R)-7: 179.5 (COOH); 175.0 (COOMe); 132.1 (C(2)); 125.7 (C(3)); 51.9 (COOMe); 41.9 (C(4)); 39.4 (C(1)); 38.5 (C(a)); 33.9 (C(b)); 25.3 (C(5)); 23.4 (C(6)); 16.0 (MeÀC(b)); minor (20%) (AE)-rel-(bR,1S,4S)-7: 179.5 (COOH); 171.4 (COOMe); 131.6 (C(2)); 126.1 (C(3)); 51.8 (COOMe); 42.0 (C(4)); 40.9 (C(1)); 38.0 (C(a)); 33.8 (C(b)); 25.5 (C(5)); 24.4 (C (6) (6)); 1.56 ± 1.48 (m, HÀC (1)); ; calc. 249.1097244).…”

“…The Ireland-Claisen rearrangement of O-allyl-substituted ketene O,O-acetals can be brought about at considerably lower temperatures [13]. Therefore, we decided to develop a synthetic access to substituted O-butadienyl-O-(trialkylsilyl)substituted ketene O,O-acetals of acetic acid and to study their reactivity in the reaction sequence Diels-Alder reaction/Ireland-Claisen rearrangement [14].…”

“…1 H-NMR (400 MHz, CDCl 3 ): 6.49 (dd (only two signals of the q are resolved), 3 J(1,2) 12.1, 4 J(1,3) % 5 J(1,4a) % 5 J(1,4b) 0.6, HÀC(1)); 6.23 (dddd, 3 J(3,4b) 16.9, 3 J(3,2) 11.0, 3 J(3,4a) 10.3, 4 J(3,1) 0.6, HÀC(3)); 5.83 (ddt, 3 J(2,1) 12.1, 3 J(2,3) 11, 4 J(2,4a) % 4 J(2,4b) 0.7, HÀC(2)); 5.09 (ddt, 2 J(4b,4a) 1.7, 3 J(4b,3) 16.9, 4 J(4b,2) % 5 J(4b,1) 0.7, H b ÀC(4)); 4.93 (ddt, 2 J(4a,4b) 1.7, 3 J(4a,3) 10.3, 4 J(4a,2) % 5 J(4b,1) 0.6, H a ÀC(4)); 3.81 (q, 3 J(2',3') 6.6, HÀC(2')); 1.52 (d, 3 J(3',2') 6.6, Me(3')); 0.95 (s, t BuSi); 0.17 (s, Me 2 Si). 13 4-(Methoxycarbonyl)-a-methylcyclohex-2-ene-1-acetic Acid (5). Methyl acrylate (5 ml, 50 mmol) was added under Ar to 4 (1.2 g, 5 mmol) and hydroquinone (85 mg, 1 mmol).…”

“…(15 ml) and NaCl soln. (15 ml), dried (Na 2 SO 4 ) and evaporated and the yellow oil purified by FC (hexane/AcOEt 8 : 2): 1.56 g (80%) of pure diazo ketone as an isomer mixture 44 : 35 : 21 by 13 C-NMR). Yellow oil.…”