13α-取代-去-C-环-19-去亚甲基-1α,25-二羟基维生素D_3类似物的合成

以维生素D3为起始原料,经臭氧化,Baeyer-Villiger氧化内酯化,开裂六元环,二氧化钌(RuO2)引进C-25位羟基,最后经Horner-Wittig反应偶合D环和A环得到13-取代-去-C-环-19-去亚甲基-1α,25-二羟基维生素D3类似物(12a,12b).     

随机排列最优成组剖分的算法

本文研究随机排列的最优成组剖分问题。这一问题源于铁路列车的最优调度计划方法的设计问题。寻找切实可行的有效算法是问题的焦点。1978年这一问题被列入文献的公开问题之一。1986年许国志、陈庆华和刘继勇提出猜测:此乃NP-完全问题,即多项式时间的算法可能不会存在,除非NP=P。 本文引入一种强同构剪枝策略,以标号树形上的隐式枚举法为工具,得到了上述问题精确最优解的一个算法。其计算时间复杂度为O(n³2^n-2),其中n为随机排列中相异数字的个数。算法在给定n的条件下,     

The di-π-methane rearrangement of systems with simple vinyl moieties : Mechanistic and exploratory organic photochemistry

3,3-Dimethyl-1,1-diphenyl-1,4-pentadiene and two 5-substituted derivatives were synthesized and studied. The regioselectivity, stereochemistry, quantum efficiency, multiplicity, and excited state reaction rates were studied in each case. The parent hydrocarbon, 5-MeO-derivative, and 5-cyano-diene—all rearranged on direct irradiation to give vinylcyclopropanes. The first compound led to 3,3-dimethyl-2,2-diphenyl-1-vinylcyclopropane. The second afforded 3,3-dimethyl-2,2-diphenyl-1-(2'-methoxyvinyl)cyclopropane. The last gave 1-cyano-3,3-dimethyl-2-(2',2'-diphenylvinyl)cyclopropane. Thus, the vinyl and methoxyvinyl groups survive in the products intact, while the cyanovinyl group is incorporated in the three-ring. In the two substituted dienes, cis-reactant gave cis-product and trans-reactant gave trans-product, both where the substituent was on the vinyl group of the product and where it became a ring substituent. The substituted di-π-methane systems underwent only cis-trans isomerization on sensitization, while the parent, unsubstituted diene led to di-π-methane product on sensitized as well as direct photolysis. While the quantum yields for the hydrocarbon diene were the same at room temperature for the direct and sensitized runs, only the sensitized runs showed a temperature dependence of efficiency with a dramatic, 5-fold increase on a 46° temperature increase. Thus, evidence was obtained for a singlet rearrangement in all cases and a triplet process only in the case of the unsubstituted diene. A sizable activation energy was seen for the triplet but not for the singlet. The room temperature quantum yields in the direct irradiations were: φ(parent diene)=0.011, φ(trans-methoxydiene)=0.051, φ(cis-methoxy-diene)= 0.050, φ(trans-cyanodiene)=0.36, and φ(cis-cyano-diene) = 0.20. A competing side reaction was cis-trans isomerization but these quantum yields were lower. Single photon counting was employed to obtain excited singlet reaction and decay rates at low temperature (i.e. 77°K) and the method of magic multipliers was used to obtain room temperature rates. These were: k_r(parent diene) = 4.7 × 10⁸ sec^?1, k_r(trans-cyano-diene)= 1.5 ×10¹⁰ sec^?1, k_r(cis-cyano-diene)= 8.0 × 10⁹sec^?1, and k_r(trans-methoxy-diene) = 1.9 × 10⁹ sec^?1. The results are discussed in terms of excited state molecular structure.An SCF-CI molecular orbital treatment of the reaction was developed. This used a cyclopropyldicarbinyl diradical species, with Walsh cyclopropane basis orbitals, as representing the half-reacted species. The energy of formation of this species from vertical excited state reactant was calculated for all three dienes and an excellent correlation with observed excited singlet rates was obtained. Similarly, dissection of the excited diradical energy into bond components led to a correlation between regioselectivity and weakness of the three-ring bond broken in the regioselectivity-determining step. Evidence was adduced for localization of the excitation energy in S₁ of reactant in the diphenylvinyl chromophore with migration of electronic excitation into the cyclopropyldicarbinyl diradical moiety during the vinyl-vinyl bridging process. A general method for quantitatively partitioning excitation energy was developed and applied to the case in hand. Finally, there was predicted a greater probability of di-π-methane three-ring fission in the excited state compared to the diradical ground state where Grob fragmentation proved energetically more favorable.