分子内环加成的甾体全合成

近年来,分子内环加成反应已广泛用于甾体化合物全合成,其主要一步是由取代的苯并环丁烯热裂而成的5,6-二亚甲基-1,3-环己二烯发生区域专一和立体选择性的环加成反应,构成甾体骨架。现在用此法已合成了一系列消旋和光学活性的甾体化合物。     

A new synthesis of highly functionalized 2H-pyran derivatives

Ethyl oxo-(2-oxo-cycloalkyl)-ethanoates undergo a smooth reaction with triphenylphosphine and dialkyl acetylenedicarboxylates via intramolecular Wittig reaction to produce spiro-cyclobutene derivatives. These spiro systems undergo electrocyclic ring opening reaction to produce electron-deficient 1,3-dienes, which spontaneously cyclize to 2H-pyran derivatives.     

Reduced classical trajectory equations for electronically non-adiabatic transition on photochemical pericyclic reactions

It may be difficult to use the classical trajectory equations (CTE) for the estimation of electronically non-adiabatic transition probabilities in photochemical pericyclic reactions because of many nuclear degrees of freedom. In order to avoid this difficulty, the CTE were reformulated in terms of the reaction path coordinates, and the reduced CTE were derived, in which the system was restricted to move one-dimensionally along the postulated reaction path. As an application, the non-adiabatic decay from the lowest excited state to the ground state was investigated for the conrotatory and disrotatory processes of the photochemical electrocyclic reaction of 1,3-cis-butadiene to form cyclobutene.     

环丙基卡宾重排为环丁烯机理的密度泛函研究

采用 B3LYP 方法,用 6-311G(d)基组计算了环丙基卡宾重排为环丁烯的反应物、过渡态和产物的能量和振动频率,并用 IRC 计算验证了过渡态。结果表明环丙基卡宾的重排机理不同于通常碳正离子重排采用的亲核重排机理,而是一个亲电重排机理。     

Photochemical transformations of 3-alkyl-3-ferrocenylcyclopropenes

Photolysis of 3-ferrocenyl-3-methyl- and 3-ferrocenyl-3-isopropylcyclopropenes was studied. Sensitized irradiation (triplet excitation) afforded [2+2]-cycloaddition products, viz., tricyclohexane derivatives. Direct irradiation (singlet excitation) of methyl-substituted ferrocenylcyclopropene gave rise to 2-ferrocenylbut-1-en-3-yne and trans-2-ferrocenylbut-2-ene. The isopropyl analog was converted into 1-ferrocenyl-4,4-dimethylcyclobutene. The reaction of this cyclopropene with 2-ferrocenyl-3-methylbut-1-ene afforded 1,3-diferrocenyl-3-isopropyl-6,6-dimethylcyclohexene. The latter compound and 3,6-diferrocenyl-3,6-diisopropyltricyclo[3.1.0.0^2,4]hexane were studied by X-ray diffraction analysis. Possible reaction pathways are discussed.     

Synthesis of Cyclobutenes and Allenes by Cobalt‐Catalyzed Cross‐Dimerization of Simple Alkenes with 1,3‐Enynes

Cobalt‐catalyzed cross‐dimerization of simple alkenes with 1,3‐enynes is reported. A [2+2] cycloaddition reaction occurred, with alkenes bearing no allylic hydrogen, by reductive elimination of a η³‐butadienyl cobaltacycle. On the other hand, aliphatic alkenes underwent 1,4‐hydroallylation by means of exo‐cyclic β‐H elimination. These reactions can provide cyclobutenes and allenes that were previously difficult to access, from simple substrates in a highly chemo‐ and regioselective manner.     

气相中环丁烯负离子与N2O反应机理的理论研究

采用B3LYP 和MP2两种计算方法,在6-31++G(d, p)的基组下,对气相中环丁烯负离子与N2O反应的微观机理进行了较为系统的计算研究。结果表明,该反应存在两条反应通道,每条反应通道又包含着三条反应路径,产物分别为乙烯基重氮甲基负离子与甲醛,同时也应能检测到少量的环丁烯酮负离子及N2等产物。其中,通道1是主反应通道,路径1为主反应路径,路径3是路径1、2的竞争反应。理论计算结果与实验预测基本一致。     

Synthesis of carborane-fused cyclobutenes and cyclobutanes

Transmetalation of carborane-fused zirconacycles to Cu(Ⅱ) induces the C-C coupling reaction to form four-membered rings. This serves as a new efficient and general methodology for the generation of a series of carborane-fused cyclobutenes and cyclobutanes. A reaction mechanism involving transmetalation to Cu(Ⅱ) and reductive elimination is proposed.