Alkynylzirconation of alkynes and application to one-pot bisalkynylation of alkynes

Stereocontrolled alkynylzirconation of unactivated alkynes was achieved by the reaction of an alkyne with Cp2ZrEt2 and alkynyl halide in this order. After hydrolysis of the alkynylzirconation product, trisubstituted enyne derivatives were obtained in good yields. Functionalized enynes were also prepared by the reaction of the alkynylzirconation products with a variety of electrophiles. Subsequent addition of the second alkynyl halide to the alkynylzirconation products provided an in situ protocol for bisalkynylation of alkynes into (Z)-enediynes in good yields.     

Some triplet energy-transfer reactions initiated by photoexcitation of triplet excited state of dibenz[a,h]anthracene to the higher triplet excited states

Some triplet energy-transfer reactions initiated by photoexcitation of the triplet excited state of dibenz[a,h]anthracene to higher triplet excited states (DBA(T_n)) were observed in the presence of the triplet energy quenchers (Q) such as naphthalene, biphenyl, p-dichlorobenzene, and o-dicyanobenzene. In the case of carbon tetrachloride (CCl₄) as Q, DBA(T_n)-sensitized decomposition of CCl₄ occurred.     

Kinetics of transient end-to-end contact of single-stranded DNAs

The formation of the pyrene (Py) dimer radical cation (Py(2)(*+)) was used to measure the kinetics of the intrastrand end-to-end contact rates of single-stranded DNAs (ssDNAs) in the 10 nanoseconds to the tens of microseconds time range. ssDNAs labeled with Py at both ends with the lengths of 3, 6, and 9 mer were synthesized, and the two-photon ionization method was employed to generate a Py(*+), which enables the measurements of the end-to-end contact rates from 10 ns. The formation rate of Py(2)(*+) depended on the length and the sequence of the ssDNAs, and about 1 order of magnitude faster rates were observed for the T-rich ssDNAs compared to those for the corresponding length of A-rich ssDNAs, showing that ssDNA made from adenines is much more rigid than that composed of thymidines. As for the T-rich ssDNAs, the formation of Py(2)(*+) attributed to the misfolded structures was also observed, which is consistent with the configurational diffusion model suggested by Ansari and co-workers.     

Lifetime regulation of the charge-separated state in DNA by modulating the oxidation potential of guanine in DNA through hydrogen bonding

A series of naphthalimide (NI)- and 5-bromocytosine ((br)C)-modified oligodeoxynucleotides (ODNs) were prepared, and their lifetimes of the charge-separated states during the photosensitized one-electron oxidation of DNA were measured. Various lifetimes of the charge-separated states were observed depending on the sequence and the incorporation sites of (br)C, and the oxidation potential of G in the (br)C:G base-pair relative to that of G in the C:G base-pair and in the GGG sequence was determined by comparing the lifetimes of the charge-separated states. The change in the cytosine C5 hydrogen to bromine resulted in a 24 mV increase in the oxidation potential of G in the (br)C:G base-pair as compared to that of G in the C:G base-pair, the value of which is comparable to a 58 mV decrease in the oxidation potential of G in the GGG sequence. These results clearly demonstrate that hole transfer in DNA can be controlled through hydrogen bonding by introducing a substituent on the cytosine.     

Fluorescence properties of 2-aminopurine-cytidine-7-deazaguanine (5'-ApCdzG-3') trimer in B- and Z-DNA

The electron transfer quenching of 2-aminopurine by guanine and 7-deazaguanine was investigated in B- and Z-DNA, and an increase in the fluorescence intensity of 2-aminopurine upon B- to Z-DNA transition was demonstrated.     

Long-lived charge-separated state leading to DNA damage through hole transfer

The hole transfer causes the long-lived charge-separated state in DNA during the photosensitized one-electron oxidation of DNA. The combination of the transient absorption measurement and DNA damage quantification by HPLC clearly demonstrated that the yield of the DNA damage correlates well with the lifetime of the charge-separated state.     

Intermolecular coupling of alkynes, isocyanates, and acyl chlorides: an efficient method for the synthesis of 5-hydroxypyrrol-2(5H)-ones

New insights into the reaction of diethylzirconocene with an alkyne, an isocyanate, and an acyl chloride in this order are reported. The products of 5-hydroxypyrrol-2(5H)-ones are obtained in good yields after hydrolysis. It is an efficient method for the synthesis of 5-hydroxypyrrol-2(5H)-ones.     

Selective linear triene formation from different alkynes using Zr/Cu system

Selective synthesis of linear trienes from three different alkynes was achieved in one-pot procedure using the Zr/Cu system. Zirconacyclopentadiene prepared from two different alkynes such as an alkyl-substituted alkyne and an aryl-substituted alkyne reacted with NCS gave chlorodienylzirconocene. It reacted with the third alkyne with electron-withdrawing groups in the presence of CuCl to afford the corresponding linear triene.     

Direct cycloauration of 1-(2-pyridylamino and 2-pyrimidinylamino)naphthalene and 2-(p-toluidino)quinoline with sodium tetrachloroaurate(III)

1-(2-Pyridylamino and 2-pyrimidinylamino)naphthalene (abbreviated as Hpyn and Hpmn, respectively) and 2-(p-toluidino)quinoline (Htlq) were directly cycloaurated with Na[AuCl₄] to give [AuCl₂L] (L = pyn, pmn, or tlq). These complexes were characterized spectroscopically and the square planar structure of [AuCl₂(pmn)] was determined by X-ray analysis. The naphthalene ring was aurated at position 2, forming a six-membered auraheterocycle with concomitant coordination of the pyrimidine-N atom. The trans influence of the carbon donor was clearly reflected in the Au–Cl bond lengths; 2.372(2) trans to C and 2.275Å trans to N. Similar square planar structures were suggested for the other two complexes.