Abstract:The Wittig reaction of (1-adamantylmethylidene)triphenylphosphorane (Ph(3)P=CH(1-Ad)) with benzaldehyde was investigated, and the results were compared with those of other ylides. The substituent effect in the reaction of the ylide with benzaldehydes was determined by competition experiments, which gave a Hammett rho value of 3.2. The rho value is much larger than those reported for analogous reactions of Ph(3)P=CH(CH(2))(2)CH(3) (rho = 0.20) and Ph(3)P=CH(CH(3))(2) (rho = 0.59), indicating that the reaction m… Show more
“…As expected, when 1b (1 equiv) reacted with 11 (6 equiv) and 2 (3 equiv) in the presence of the oxygen within 5−10 min, the only product is ( E )-1-adamantyl-2-(4-methoxyphenyl)ethene 12 and the yield is 100% when the crude mixture was analyzed by the proton NMR (eq 4). This result indicates that the same adamantyl radical actually could be generated by using 11 , 2 , and air at room temperature. , …”
Section: Resultsmentioning
confidence: 62%
“…It has been reported that different alkyl radicals including 1-adamantyl radical and aryl radical can be generated by the reduction of alkyl or aryl halides with (ethylenediamine)chromium(II) complexes in dry dimethylformamide . The palladium-catalyzed reaction of 1-bromoadamantane with styrene and donor-substituted styrenes give the corresponding Heck-type coupling product ( E )-1-adamantyl-2-arylethene in 15−41% also has been reported by Bräse et al Similarly, Yamataka and co-workers also have reported that both ( Z ) - and ( E )-1-adamantyl-2-arylethene mixture had been prepared from the Wittig reaction of substituted benzaldehydes with (1-adamantylmethylidene)triphenylphosphorane …”
Reactions of (E)-beta-nitrostyrenes 1 and triethylborane 2 or tricyclohexylborane 4 in THF solution at room temperature in the presence of oxygen in the air as radical initiator generate high yields of trans-alkenes (E)-3 or (E)-5. Medium to high yields of different (E)-alkenes (E)-5, 7, 10, 12, and 14 also can be prepared when 1 reacts with different radicals, prepared from secondary alkyl iodides 6 and 8 or tertiary alkyl iodides 9, 11, and 13, in the presence of 2 and air as radical initiator. The generation of the only product (E)-alkenes can be explained by the generation of the benzylic radical A and/or B as the intermediate only and the mechanism is similar to Scheme 1. Both (E)- and (Z)-16a-c are generated when (E)- and (Z)-15a-c are used to react with adamantyl radical under similar conditions. Only (Z)-16d was observed when either (E)- or (Z)-15d was used to react with adamantyl radical. The generation of the (E)- and/or (Z)-alkenes can be explained by the free rotation of the A and/or B to generate A' and/or B' and vice versa, and the mechanism is proposed to be a free-radical reaction via NO2/alkyl substitution and is shown as Scheme 2.
“…As expected, when 1b (1 equiv) reacted with 11 (6 equiv) and 2 (3 equiv) in the presence of the oxygen within 5−10 min, the only product is ( E )-1-adamantyl-2-(4-methoxyphenyl)ethene 12 and the yield is 100% when the crude mixture was analyzed by the proton NMR (eq 4). This result indicates that the same adamantyl radical actually could be generated by using 11 , 2 , and air at room temperature. , …”
Section: Resultsmentioning
confidence: 62%
“…It has been reported that different alkyl radicals including 1-adamantyl radical and aryl radical can be generated by the reduction of alkyl or aryl halides with (ethylenediamine)chromium(II) complexes in dry dimethylformamide . The palladium-catalyzed reaction of 1-bromoadamantane with styrene and donor-substituted styrenes give the corresponding Heck-type coupling product ( E )-1-adamantyl-2-arylethene in 15−41% also has been reported by Bräse et al Similarly, Yamataka and co-workers also have reported that both ( Z ) - and ( E )-1-adamantyl-2-arylethene mixture had been prepared from the Wittig reaction of substituted benzaldehydes with (1-adamantylmethylidene)triphenylphosphorane …”
Reactions of (E)-beta-nitrostyrenes 1 and triethylborane 2 or tricyclohexylborane 4 in THF solution at room temperature in the presence of oxygen in the air as radical initiator generate high yields of trans-alkenes (E)-3 or (E)-5. Medium to high yields of different (E)-alkenes (E)-5, 7, 10, 12, and 14 also can be prepared when 1 reacts with different radicals, prepared from secondary alkyl iodides 6 and 8 or tertiary alkyl iodides 9, 11, and 13, in the presence of 2 and air as radical initiator. The generation of the only product (E)-alkenes can be explained by the generation of the benzylic radical A and/or B as the intermediate only and the mechanism is similar to Scheme 1. Both (E)- and (Z)-16a-c are generated when (E)- and (Z)-15a-c are used to react with adamantyl radical under similar conditions. Only (Z)-16d was observed when either (E)- or (Z)-15d was used to react with adamantyl radical. The generation of the (E)- and/or (Z)-alkenes can be explained by the free rotation of the A and/or B to generate A' and/or B' and vice versa, and the mechanism is proposed to be a free-radical reaction via NO2/alkyl substitution and is shown as Scheme 2.
“…Relative overall reaction rates for the examined reaction were determined by experiments using competition Hammett methodology . The ratios of particular vinylphosphonium salts 10 were determined from their yields when α‐tributyl‐ [(trimethylsilyl)‐methylene]phosphorane 8 were allowed to compete with benzaldehyde 9a and with one or two selected p ‐substituted derivatives 9b–j in the same reaction mixture.…”
The mechanism of the reaction of tributyl[(trimethylsilyl)methylene]phosphorane with benzaldehyde and its p‐substituted analogues has been examined. It has been found that the electronic nature of the p‐substituents in aromatic aldehydes strongly influences the stereochemical and kinetic outcome of the Peterson olefination whereas temperature substantially affects their Hammett correlation. This indicates that the Peterson olefination is a multistep reaction involving the formation of at least an oxyanion/betaine and a carbanion as intermediates. In turn, moderate Z‐selectivity might be the result of “steric approach intermediate control”; however, E‐selectivity seems to result from the silicon–oxygen interaction and interactions of steric substituents in competing erythro‐ and threo‐betaines.
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