.alpha.,.beta.-Unsaturated Acetals as Precursors of .alpha.-Substituted Ethoxy Dienes. Useful Reagents for Nucleophilic Acylation
摘要:
The reaction of (E)-1,1-diethoxybut-2-ene (1a) and 1,1-diethoxy-3-methylbut-2-ene (1b) with 2 equiv of sec-butyllithium complexed with potassium tert-butoxide (Schlosser's base) in THF at -95 degrees C gives 1-metalated 1-ethoxy 1,3-dienes that are synthetically equivalent to acyl anions. Subsequent reaction with suitable electrophiles, such as alkyl halides, aldehydes, ketones, carbon dioxide, and carboxylic acid derivatives, affords (E)-1-substituted 1-ethoxy 1,3-dienes 2a-i. Experimental procedures are given for the reaction of the carbanionic intermediates with the electrophiles. Some typical examples for the conversion of the produced alpha-substituted alkoxy dienes into the corresponding alpha,beta-unsaturated carbonyl compounds are also reported. In particular, in the case in which crotonaldehyde is used as an electrophile, the addition product 2c undergoes acid-catalyzed conversion to compounds 4c, 5c, and 6c as a function of the experimental conditions.
LIC-KOR promoted formation of conjugated dienes as useful building blocks for palladium-catalyzed syntheses
作者:Annamaria Deagostino、Manuele Migliardi、Ernesto G. Occhiato、Cristina Prandi、Chiara Zavattaro、Paolo Venturello
DOI:10.1016/j.tet.2005.01.044
日期:2005.3
It is demonstrated that α,β-unsaturated acetals can be considered a synthetic tool for transforming carbonyl derivatives into cheap and easily accessible starting materials for the construction of various and more complex structures. The lithium–potassium mixed superbase LIC-KOR induces a conjugate elimination reaction that converts α,β-unsaturated acetals into 1E-1-alkoxybuta-1,3-dienes. These derivatives
已经证明,α,β-不饱和缩醛可以被认为是用于将羰基衍生物转化成廉价且易于获得的起始材料以用于构建各种和更复杂的结构的合成工具。锂-钾混合超碱LIC-KOR引起共轭消除反应,该反应将α,β-不饱和缩醛转化为1 E -1-烷氧基丁1,3-二烯。这些衍生物可以很容易地就地金属化并通过与亲电试剂反应而官能化。结果可分为两部分:(1)烷氧基二烯基硼酸酯与四氢萘醌或异苯并二氢吡喃酮衍生的乙烯基三氟甲磺酸酯之间的钯催化交叉偶联反应;(2)在钯催化剂的存在下与芳基衍生物的区域和立体选择性交叉偶联反应(Heck条件)。
A Short and Efficient New Synthesis of γ-Halo-Substituted α,β-Unsaturated Acetals and Carbonyl Compounds
Treatment with N-bromosuccinimide (NBS) or N-chlorosuccinimide (NCS) of 1-subsituted 1-alkoxy-1,3-dienes, obtained by reaction of α,β-unsaturated acetals with LICKOR superbase, affords γ-brominated (chlorinated) α,β-unsaturated acetals or carbonyl compounds, according to the selected experimental conditions.
α,β-Unsaturated acetals afford, in the presence of the LIC-KOR superbase and of a suitable electrophile, 1-functionalized-1-alkoxybuta-1,3-dienes. These substrates cross couple with aryl derivatives in the presence of a Pd catalyst (Heck conditions) in a regio- and stereoselective mode using different ionic liquids as a solvent.
Heck functionalization of azadipyrromethenes (aza-DIPY) allows the introduction of suitable functional groups to convert aza-BODIPY in bioconjugate complexes.
Synthesis of Highly Functionalised Dihydrobenzofurans and Indolines by Palladium-Catalysed Mizoroki-Heck-Heteroannulation Cascade Reactions of Alkoxy-1,3-dienes
A Mizoroki–Heck–heteroannulationcascadereaction has been used to prepare substituted dihydrobenzofurans and indolines in good yields by the reaction between functionalisedalkoxy-1,3-dienes and several o-iodophenols or protected o-iodoanilines.