The parent 5H-indazolo[3,2-b]benzo[d]-1,3-oxazine heterocycle as well as a series of novel analogues have been synthesized utilizing two subsequent intramolecular heterocyclizations in one pot. A variety of diversity groups were added to explore the scope of this reaction and to provide a number of new compounds for biological screening.
The novel heterocycle 2,3-dihydrooxazolo[3,2-b]indazole has been synthesized and utilized to provide easy access to 1H-indazolones, particularly the previously unreported 2-(2-alkoxyethyl)-1H-indazol-3(2H)-ones. Mechanistic as well as optimization and reaction scope studies are reported.
The sudden transition from in-person to virtual learning during the spring 2020 semester posed challenges for students and faculty alike. This paper explores the techniques used by faculty to transform the chemistry and biochemistry curriculum at a Hispanic-serving institution with a significant proportion of firstgeneration students and the response of students to these changes. Faculty utilized an assortment of techniques, including synchronous lectures by video conference, asynchronous prerecorded lectures, online examinations with varying timing policies, and virtual office hours. A survey was completed by 332 students across 26 different courses taught by 11 faculty regarding their preferences for course delivery format and the academic and nonacademic challenges they faced. A paired samples t-test indicated a statistically significant difference in satisfaction with face-to-face instruction (M = 4.13, SD = 0.765) and satisfaction with virtual instruction (M = 3.57, SD = 0.961), t(440) = 13.30, p < 0.001, Cohen's d of 0.63, and Cronbach's α of 0.767. The results indicated a preference for face-to-face instruction. Open-ended survey questions identify that the primary academic challenges faced by students involved technology, understanding material, and difficulty obtaining help, while the primary nonacademic challenges were work issues, focus/motivation, and family issues. These results may inform future practices for virtual instruction.
A course entitled “Careers in Chemistry” has been developed and implemented in the chemistry curriculum. This seminar-style class exposes students to a full spectrum of career options available to chemists by hosting outside speakers. The workings and logistics of this course and its positive impact on students are described. Survey results suggest that implementation of a similar course or seminar series at other institutions may be beneficial in exposing students to career options in chemistry.
Irradiation of 1,2-dimethyl-3-hydroxyquinolinone (DMQ) leads to excited state intramolecular proton transfer (ESIPT) generating an 3-oxidoquinolinium species which undergoes [3+2] photocycloaddition with dipolarophiles. A parallel, fluorescence quenching assay using a microplate format has been developed to evaluate fluorescence quenching of this species with a range of dipolarophiles.We have reported excited state intramolecular proton transfer (ESIPT) 1 of 3-hydroxyflavone (3-HF) derivative 1 and photochemical [3+2] cycloaddition of the derived oxidopyrylium 2 species 2 with methyl cinnamate 3 (Figure 1). 3 The resulting cycloadduct 4 was subsequently transformed to the natural product methyl rocaglate 5. Nitrogen analogues of 3-hydroxyflavone including 1-methyl-2-methyl-3-hydroxyquinolinone (DMQ) (6) 4 have been reported to undergo ESIPT to afford 3-oxidoquinolinium 7. 5 This precedent prompted us to investigate the feasibility for photocycloaddition of oxidoquinolinium intermediates such as 7 with a variety of dipolarophiles as reaction partners.In order to study the cycloaddition reactivity of DMQ 6 under UV irradiation in the presence of various dipolarophiles, we considered a parallel screening approach. A number of recent reports have outlined use of fluorescent probes for high throughput reaction development. 6 Our initial plan was to take advantage of the inherent photochemical behavior of 6 to implement a parallel, fluorescence quenching assay. Under UV irradiation, 3-hydroxyquinolinone 6 undergoes rapid proton transfer (ns timescale) from its first excited state 6* leading to the formation of phototautomer species 7* which decays to 7 via fluorescence emission at 470 nm (Figure 2 should provide an indication of photocycloaddition reactivity. 8 In this paper, we report development of a parallel, fluorescence quenching assay using a microplate format to evaluate fluorescence quenching of this species with a range of dipolarophiles and correlation of the photophysical data with preparative photocycloadditions.We first investigated the photophysical properties of 3-hydroxyquinolinone 6. UV/Vis spectra of 6 in various solvents showed an absorbance maximum at 370 nm ( Figure 3) 8 which was well separated from absorbances of most commonly encountered dipolarophiles such that selective light absorption by the heterocycle could be easily accomplished. Upon excitation at 350 nm, dual fluorescence associated with normal excited state 6* (400 nm) and tautomeric excited state 7* (470 nm) was observed. The latter emission related to ESIPT was characterized by an unusually large Stokes shift as expected and previously reported (Figure 3). 4d The origin of this ESIPT emission was also confirmed by excitation spectra recorded at 470 nm and were found to be identical to the corresponding absorption spectra. 8 The species 7* was also observed to have a fluorescence lifetime of 16.8 ns and a very high quantum yield of 0.65 in 1,4-dioxane. 8 The latter lifetime should make 7* a trappable species in comparison...
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