Reaction of trisubstituted alkenes with iron porphyrin carbenes: facile synthesis of tetrasubstituted dienes and cyclopentadienes
作者:Peng Wang、Saihu Liao、Sunewang R. Wang、Run-Duo Gao、Yong Tang
DOI:10.1039/c3cc44092c
日期:——
The unprecedented reaction of trisubstitutedalkenes with iron porphyrin carbenes has been successfully developed. Both multiply substituted 1,3-butadiene and cyclopentadiene products are readily accessible with high efficiency and selectivity in good yields.
Synthesis of α,β-Unsaturated Ketones Using Allylidenetriphenylphosphorane as a Three-carbon Unit
作者:Minoru Hatanaka、Ritsuo Imashiro、Ikuo Ueda
DOI:10.1246/cl.1992.2253
日期:1992.11
3-Alkoxycarbonyl-2-ethoxy-2-propenylidenetriphenylphosphorane reacts in turn with alkyl halides and aldehydes in the presence of base via a one-pot procedure to give moderate to good yields of conjugated enol ethers. Hydrolysis of the conjugated enol ethers and subsequent decarboxylation provide a novel route to α,β-unsaturated ketones.
penylidene)triphenylphosphorane reacted with diacylethylenes to give 2-ethoxycyclopentadienes as a 1:1 mixture of the 1,3- and 1,4-dienes, which were converted upon mild acid treatment into cyclopentenones in a single form. Use of acylmethylenemalonate as an unsymmetrical substrate provides an excellent route to substituted cyclopentenones. An application of the annulation to synthesis of (±)-methyl
Allylidenetriphenylphosphorane as a bifunctional reagent: synthesis of cyclopentenones and .alpha.,.beta.-unsaturated ketones with [3-(alkoxycarbonyl)-2-ethoxy-2-propenylidene]triphenylphosphorane
When (3-(ethoxycarbonyl)-2-ethoxy-2-propenylidene) triphenylphosphorane (6) was allowed to react with cu-bromo ketones 8a-d in dichloromethane in the presence of Cs2CO3 at room temperature, a [3 + 2] annulation occurred and led to the formation of the corresponding 2-ethoxycyclopentadienes 9a-d in excellent yields. Similarly, bromo thioester 8g underwent the annulation to give 4-(ethylthio)-cyclopentadiene 9g. Secondary bromides 2-bromo-3-pentanone and 2-bromocyclohexanone also afforded tetrasubstituted cyclopentadienes 9e and 9f in moderate yields when 2 equiv of 6 was used. The annulation is believed to proceed through a sequence involving a stepwise alkylation at the gamma position of 6 and an intramolecular Wittig reaction because of the fact that intermediate 11 was isolated. The resulting 2-ethoxycyclopentadienes 9a-g were converted quantitatively into the corresponding cyclopentenones 10a-g upon mild acid treatment. Furthermore, allylidenetriphenylphosphorane underwent a carbon elongation at both ends of the three-carbon unit via an alkylation-Wittig reaction sequence. (3-(tert-Butoxycarbonyl)-2-ethoxy-2-propenylidene)triphenylphosphorane (7) reacted first with alkyl halides and then with aldehydes in the presence of Cs2CO3 to give enol ethers 23a-f, which were converted into alpha,beta-unsaturated ketones 20, 21, and 25c-f by hydrolysis of the enol ether and then decarboxylation. In this way, shogaol (29), the pungent principle component of ginger, was conveniently synthesized starting from 2-methoxy-4-methylphenol.