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Relevant academic research and scientific papers

Use of Hine's D Values To Predict the Position of the Equilibrium in the Cope Rearrangement of Multiply Substituted 1,5-Dienes

A series of 1,5-dienes (1a-f) were employed to test whether Hine's D values can predict the position of equilibrium in Cope rearrangements.In the cases of the substituent pairs , ,, , and , equilibrium constants calculated with Hine's D values gave reasonable agreement with those obtained experimentally.Dienes 1g-i were prepared to test whether reduction of the ?-donating character of a nitrogen substituent (carbamoyl vs dimethylamino) would change the directing ability of the nitrogen group.The aggregate order of directing ability was N(CH3)2 > OCH3 > EtO2CN(CH3) > CH3 > H>.Diene 15a, with a more complicated substitution pattern (OCH3 and CH3 versus CH3 and H) not directly amenable to analysis with D values, can be considered to reduce to the case of .The experimental Keq obtained agreed with that expected for the pair.Dienes 15c and 16b, designed to test the pairs and , respectively, decomposed under the gas phase conditions of the rearrangement.Attempts to effect rearrangement with Pd(II) catalysis failed.

α-OXOKETENE DITHIOACETALS AS INTERMEDIATES FOR AROMATIC ANNELATION

The α-oxoketene dithioacetals of general formula 1 (Scheme 2), undergo regioselective 1,2-addition with allyl anions to afford the corresponding carbinol acetals 6 in quantitative yields, which on treatment with BF3*Et2O in refluxing benzene yield the corresponding aromatic systems.The method has been shown to be widely applicable as exemplified by a large number of allyl anions (Scheme 3) reacting with α-oxoketene dithioacetals with wide structural variation.However, when 1 carry the α-substituent the intermediate carbinol acetals 14 (Scheme 4) follow, different path to yield the corresponding indenes 15 in good yields.The cinnamoylketene dithioacetals 16 react with allyl anions to afford the corresponding methylthiostilbenes 18 (Scheme 5), while the homologous dithioacetal 20 failed to yield the corresponding 1,4-biaryl-1,3-diene 22 (Scheme 6).This limitation was circumvented by reacting 23 with allyl anions to afford the corresponding stilbenes 24, dienes 25 and triene 26 respectively.The method was successfully extended for naphthoannelation.Thus naphthalenes 28 (Scheme 7) were prepared by reacting benzylmagnesium chloride with 1.In this case the reaction followed a sequential 1,4- and 1,2-addition mode and yielded the corresponding benzyl substituted naphthalenes.This problem was solved by reacting benzylmagnesium chloride with 8 to afford the corresponding naphthalenes 31 (Scheme 8) in excellent yields.Similarly the lithio derivatives derived from toluene followed 1,2-addition mode with 1 to afford the derived methylthionaphthalenes 39 (Scheme 9) in high yields.The other alkyl substituted naphthalenes 41, 43 (Scheme 9), 45, 47 (Scheme 10) were similarly prepared.Also 1 and β-oxodithioacetals 8 reacted with 1-naphthylmethylmagnesium chloride to afford the corresponding phenanthrenes 49 and 51 respectively in good yields.The method was extended to benzanthracene 56 (Scheme 11) synthesis successfully.The 2-naphthylmethyl magnesium chloride reacted in a sequential 1,4- and 1,2-fasion to afford the corresponding naphthylmethyl hydrocarbons 58 while it reacted with β-oxodithioacetals to give expected condensed aromatics 60, 61 and 62 (Scheme 12) in high yields.The 1-naphthylmethylmagnesium chloride also reacted with β-oxodithioacetals 23 to afford the corresponding styrylphenanthrenes 65, dienes 66 and triene 67 respectively in high yields.The intermediate 69 precursor in the synthesis of hexahelicine was also obtained by reacting 68 with 1-naphthylmethylmagnesium chloride (Scheme 13).The oxygenated benzylmagnesium halides reacted with 1 in 1,2-fasion (Scheme 14) with the exception of the formation of 79.Five fold excess of Reformatsky reagent reacted with 1 to afford the corresponding salicylates 82 (Scheme 15) in high yields.Similarly 84 (Scheme 16) was formed.Propargylmagnesium chloride also reacted with 1 with the participation of solvent methanol to afford the corresponding thioresolcinol dimethylethers 86 ...