摘要
综述了近几年来利用金属催化合成多取代呋喃环的方法。分两大类介绍:一是通过对呋喃环进行结构改造,即呋喃金属试剂在过渡金属催化下与卤化物或酰氯发生偶联反应得到,或呋喃卤化物与金属试剂、烯烃、炔烃偶联得到;二是以非环状化合物为前体进行呋喃环的构筑,即在金属试剂催化下,1,2-联烯基酮、β-碘代-β-烯酮、叁键在α,β-、β,γ-、γ,δ-的炔酮、4-炔-2-烯醇可以关环得到多取代的呋喃产物。此外,在Ru_2(OAc)_4催化下,α-叠氮酮与炔烃反应得到金属卡宾中间体,然后关环也可得到取代呋喃产物。
The regiospecific synthesis of substituted furans by metal - catalyzed methodologies is reviewed. The whole review consists two parts.
(1) Methodologies based on preformed furans
Furanyl metal reagents (M = Sn, B, Zn, Mn etc) undergo transition metal - catalyzed cross coupling reaction with organic halides or acyl chlorides to afford the substituted furans. On the another hand, furanyl halides can also undergo cross coupling reaction with orgnometallic reagents or termial alkynes to afford functionalized furans. Under the catalysis of Pd(0) , furanyl halides can also react with alkenes to produce alkenyl substituted furans.
The C - H activation reaction of furans with RuH2 (CO) PPh3 directly produced furanyl ruthenium intermediates, which can further react with certain silylsubstituted 1 - alkynes to afford 3 - substituted furans. The C - H bond activation occurred regiospecifically the 3 - positions.
(2) Methodologies based on the cyclization reaction of acyclic compounds
The most efficient way to synthesize furans is the cyclization of the corresponding acyclic precursors, which provides the diversity, efficiency, and selectivity for the substituted furans synthesized.
Under the catalysis of Ru(II) or Ag(I) ,1,2- allenyl ketone can undergo cycloisomerization to afforded 3 - unsub-stituted furans. Recently Pd(0) - catalyzed coupling- cyclization reactions of organic halides and 1,2- allenyl ketones were also developed to afford polysubstituted furans. The diversity of furan thus synthesized depends on the type of organic halides as well as the substitution patterns of 1,2- allenyl ketones.
Under the catalysis of Pd complexes, B - iodo -B- enone can undergo oxidative addition - cyclization or dimeriza-tion reaction to produce furans.
Under the catalysis of Pd, another type of acyclic starting material suitable for the synthesis of furan is alkynones, the carbon - carbon triple bond can be located at a , B - , B , r - , and r , - positions . Both cycloisomerization and two - component coupling - cyclization have been reported. ( Z) - 4 - Alkyn - 2 - enol can also be cyclized to afford polysubstituted furans, Here, the hydroxyl group acts as a nucleophile to attack the transition metal - activated C - C triple bonds.
The Ru2(OAc)4 - catalyzed reaction of a - diazo ketones with alkyne also provides an efficient route to furan derivatives. In this reaction the key intermediates are metal carbenes. Their intermolecular reaction with alkynes and the intramolecular reaction with α,β - unsaturated enones would form the furan skeletones.
出处
《有机化学》
SCIE
CAS
CSCD
北大核心
2000年第5期701-711,共11页
Chinese Journal of Organic Chemistry
关键词
过渡金属
催化合成
呋喃衍生物
transition metal, catalysis, synthesis, substituted furans
