Non-quadratic-intensity dependence of two-photon absorption induced fluorescence of organic chromophores in solution

We have provided a model to interpret the non-quadratic-intensity dependence behavior commonly observed in the two-photon fluorescence (TPF) experiment excited with high laser intensity. The model also provides one with a different technique to measure the two-photon absorption cross section of an organic chromophore in solution. In contrast to the commonly used low intensity technique that depends on the quadratic-intensity law, the present technique is based on the non-quadratic-intensity dependence of two-photon fluorescence. Auxiliary data such as two-photon quantum efficiency and fluorescence collection efficiency, essential in the low intensity method, are not required in the present technique. TPF measurements of Rhodamine B in methanol are carried out to demonstrate the validity of the present method. The method is used to determine the two-photon absorption cross section of a new chromophore attached with tricyano-derivatized furan as the electron acceptor. The two-photon absorption cross section measured using this method is also compared with that using a conventional transmission technique.     

Regioselective reduction of 3-sulfonyl glutarimides to 3,4-dihydro-5-sulfonylpyridin-2-ones. Formal synthesis of the indolizidine 8a-epi-dendroprimine

Sodium borohydride regioselectively reduced various 3-sulfonyl glutarimides 1 to hydroxy piperidones 2, which were further dehydrated to 3,4-dihydro-5-sulfonylpyridin-2-ones 3 in the presence of boron trifluoride. Formal synthesis of 8a-epi-dendroprimine (4) possessing an indolizidine ring system has been accomplished via intramolecular radical cyclization of cyclic vinyl sulfone 5.     

Formal Synthesis of (±)-Mitsugashiwalactone and (±)-Isodihydronepetalactone from Norborn-5-en-2-one Involving Shapiro Reaction

A formal synthesis of (±)-mitsugashiwalactone ( 1 ) and (±)-isodihydro nepetalactone ( 2 ) was accomplished. Baeyer-Villiger lactonization of ketone 9 followed by acidic treatment led to the rearranged lactone 8 , which underwent a series of functional group transformations to give cyclopentanone derivatives 19 and 20 . Shapiro reaction on 21 and 22 in the presence of excess dry ice gave lactones 5 and 6 . Lactones 5 and 6 previously have been converted to mitsugashiwalactone ( 1 ) and isodihydronepetalactone ( 2 ), respectively.     

Long distance laser ultrasonic propagation imaging system for damage visualization

Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms.     

A facile synthesis of 3-aryl pyroglutamic acid. Facile synthesis of baclofen and chlorpheg

A facile synthesis of 3-aryl pyroglutamic acids via stepwise [3+2] annulation and desulfonated hydrolysis is reported. Base-induced coupling/cyclization reactions of α-sulfonylacetamide with various β-functional groups of (Z)-2-bromoacrylates yielded three contiguous chiral centers on the polysubstituted pyroglutamates system with trans-trans orientation in a one-pot synthesis. This facile strategy was used to synthesize amino acid derivatives baclofen and chlorpheg.     

Efficient synthesis of fused bicyclic glutarimides. Its application to (+/-)-alloyohimbane and louisianin D

[reaction: see text] The reaction of alpha-sulfonyl acetamide 1 with various cyclic unsaturated esters 2 to fused bicyclic glutarimides is reported. Syntheses of (+/-)-alloyohimbane (4) and louisianin D (5) have been accomplished.     

Geiparvarin Analogues: Synthesis and Anticancer Evaluation of α-Methylidene-γ-butyrolactone-Bearing Coumarins

To determine some of the structural features of geiparvarin that account for its cytostatic activity in vitro, certain geiparvarin analogues modified in the furan-3(2H)-one moiety and the alkenyloxy substituent were synthesized and tested against the growth of 60 human cancer cell lines derived from nine cancer-cell types. These compounds demonstrated a strong growth-inhibitory activity against leukemia cell lines but were relatively inactive against non-small-cell lung cancers and CNS cancers. Comparison of the mean log GI₅₀ values of γ-[(E)-1-methylprop-1-enyl]-α-methylidene-γ-butyrolactones 7 – 9 revealed that 7-[(E)-3-(2,3,4,5-tetrahydro-4-methylidene-5-oxofuran-2-yl)but-2-enyloxy]-2H- 1-benzopyran-2-one ( 8 ; −5.47) was more active than its 6-substituted counterpart 7 (−5.21) and its 3-chloro-4-methyl derivative 9 (−5.31) and had a potency similar to that of geiparvarin (log GI₅₀=−5.41). These results indicated that the furan-3(2H)-one moiety of geiparvarin could be replaced by an α-methylidene-γ-butyrolactone unit without losing the anticancer potency, and that the best substitution site at the coumarin moiety was C(7). The alkenyloxy substituent of 8 was also replaced by a methoxy substituent. Among these α-methylidene-γ-butyrolactones, 7-[(2,3,4,5-tetrahydro-4-methylidene-5-oxo-2-phenylfuran-2-yl)methoxy]-2H-1-benzopyran-2-one ( 11 ) was the most potent with a mean log GI₅₀ value of −5.83 and a range value of 132 (10^2.12).     

One-pot facile conversion of Baylis-Hillman adduct into N-alkyl 3-(E)-alkylidene-5-substituted sulfonylpiperidine-2,6-dione. Formal synthesis of tacamonine

A stepwise [3+3] strategy to N-alkyl 3-(E)-alkylidene-5-substituted sulfonylpiperidine-2,6-dione 1 used various N-alkyl α-substituted sulfonylacetamides 2 and α,β-unsaturated esters 3 as starting materials. α,β-Unsaturated esters 3 were generated by Baylis-Hillman reaction. A ring closure mechanism was proposed for the reactions. This method provides a convenient formal synthesis of tacamonine.     

Total Synthesis of (±)-Boschnialactone and (±)-Tetrahydroanhydrodesoxyaucubigenin

A total synthesis of (±)-boschnialactone ( 1 ) and (±)-tertahydroanhydrodesoxyaucubigenin ( 2 ) is described and trisubstitued cyclopentenoid 3 is a key intermediate.     

Formal Syntheses of (±)-Verbenalol and (±)-Udoteatrial

A formal total synthesis of (±)-verbenalol 1 and (±)-udoteatrial 2 is described. Tie key intermediate is diiodolactone 7.