1,721,279 research outputs found
Nitrilimine cycloaddition onto 2-azetidinones bearing alkenyl dipolarophile(s)
No full textAbstract—Silver acetate-promoted nitrilimines cycloaddition onto 3(R*)-phenyl-4(R*)-cinnamoyl-2-azetidinone 1 were highly
stereoselective giving 4-(4,5-dihydropyrazol-5-yl) carbonyl-2-azetidinones 5 as the major products and regioisomeric 4-(4,5-
dihydropyrazol-4-yl) carbonyl-2-azetidinones 6 as the minor one. When the same protocol was applied to the novel 3(R*)-phenyl-4(S*)-
(4-benzoyl-E,E-1,3-butadienyl)-2-azetidinone 2 it resulted in site- and regioselective but not stereoselective cycloaddition, involving the
formation of the four cycloadducts 10–13
Synthesis of the carbazole alkaloids hyellazole and 6-chlorohyellazole and related derivatives
No full textWe describe a new seven-stage synthesis of the carbazole alkaloids hyellazole and 6-chlorohyellazole, which proceeds via thermal cyclization of the 3-(buta-1,3-dienyl)indoles 7ab and 7bb, prepared from the condensation products of indole-2,3-diones 1a, b and the 3-methyl-4-phenylbut-3-en-2-one 2b. This procedure was also used to prepare related 3-methoxy-1-phenylcarbazole derivatives
Synthesis of [a]annulated carbazoles from indol-2,3-dione
No full textReaction of ethyl chloroformate with 3-aroylmethylindol-2(3H)-ones 5 affords the ethyl 3-[(2-aryl-2-ethoxycarbonyloxy)ethenyl]-2-(ethoxycarbonyloxy)indole-1-carboxylates 6 from which the corresponding [a]annulated carbazoles 10 are obtained via 6π-electrocyclization
Nitrilimine cycloaddition to 4-(pyrazol-5-yl)carbonyl-2-azetidinone and 4-(pyrazol-4-yl)carbonyl-2-azetidinone
No full textThe higly stereoselective nitrilimine cycloaddition onto the novel 3(R*)-phenyl-4(S*)-cinnamoyl-2-azetidinone 2 gave 4-(4,5-dihydropyrazol-5-yl)carbonyl-2-azetidinone 5 as the major product and 4-(4,5-dihydropyrazol-4-yl)carbonyl-2-azetidinone 6 as the minor one. Ceric ammonium nitrate (CAN) oxidation of the cycloadducts gave the title compounds with good overall yield. (C) 2003 Elsevier Science Ltd. All rights reserved
Diastereoselective cycloadditions of nitrilimines to enantiopure acrylamides
No full textThe diastereoselective cycloaddition of the nitrilimine 2 with enantiopure acrylamides 3 was exploited to obtain enantiopure 4,5-dihydropyrazoles 4 and 5. Basic hydrolysis of the cycloadducts gave the dicarboxy derivatives 6 and 7 or 8 and 9, which are of potential interest as new chiral building blocks. (C) 2002 Elsevier Science Ltd. All rights reserved
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