1,721,263 research outputs found
Reaction of N-haloamidines with 1,1-diaminoethenes
No full textIn the context of our work on the synthesis of imidazole ring system we have studied the reaction beetween N-haloamidines and 1,1-diaminoethenes
2-Imidazolines. VI. Structural factors affecting the rearrangement rate of 4,5-diamino-2-imidazolines to N-(1,2-diaminoethylidene)amidines
No full textTandem aza-Wittig reaction/electrocyclic ring closure. 3,4-dihydroquinazoline from N-imidoyliminotriphenylphosphorane and aromatic aldehydes
No full textRecently we reported a new synthesis of quinazoline ring starting from N-imidoyliminotriphenylphosphoranes and aromatic aldehydes. The proposed mechanism was proved by an indipendent synthesis of the 1,3-diaza-1,3-diene intermediates. These diene derivatives when heated either in xilene or benzene give quantitatively the corresponding 3,4-dihydroquinazolines
Policy Optimization for CMDPs with Bandit Feedback: Learning Stochastic and Adversarial Constraints
No full textWe study online learning in constrained Markov decision processes (CMDPs) in which rewards and constraints may be either stochastic or adversarial. In such settings, Stradi et al. (2024b) proposed the first best-of-both-worlds algorithm able to seamlessly handle stochastic and adversarial constraints, achieving optimal regret and constraint violation bounds in both cases. This algorithm suffers from two major drawbacks. First, it only works under full feedback, which severely limits its applicability in practice. Moreover, it relies on optimizing over the space of occupancy measures, which requires solving convex optimization problems, an highly inefficient task. In this paper, we provide the first best-of-both-worlds algorithm for CMDPs with bandit feedback. Specifically, when the constraints are stochastic, the algorithm achievesÕ(√T ) regret and constraint violation, while, when they are adversarial, it attainsÕ(√T ) constraint violation and a tight fraction of the optimal reward. Moreover, our algorithm is based on a policy optimization approach, which is much more efficient than occupancy-measure-based methods
European Colloquium on Heterocyclic Chemistry
No full textThe reaction beetween N-haloamidines and 1,1-diaminoethenes gave 1,2-diaryl-4-amino-5-chloroimidazoles. The 1,2-diaryl-4-aminoimidazoles were obtained by reduction of the corresponding 5-chloroderivatives
A new synthesis of quinazoline ring
No full textIn this communication we report our results about the reaction of S,S-dimethyl-N-(N-benzimidoyl)sulfimides with enamines. The reaction, wich occurs at high temperaure, affords in good yields 2-aryl-4-alkylquinazolines and 2-aryl-4,4-disubstituted-3,4-dihydroquinazolines depending on the enamine employed
Carotenoids in bird plumage: the complement of red pigments in the plumage of wild and captive bullfinch (Pyrrhula pyrrhula)
No full textWe have studied the carotenoid pigments in the red plumage of male bullfinch (Pyrrhula pyrrhula) immediately following capture and after the completion of the moult in captivity under dietary control. Astaxanthin, adonirubin, and α-doradexanthin, as well as papilioeritrinone and canthaxanthin (in lower amounts) are in every case the dominant carotenoids in the plumage pigment of wild individuals. α-Doradexanthin is responsible for the reddish-rose colour, which captive individuals adopt after a diet consisting mainly of lutein as disposable carotenoid. The red pigmentation biogenesis of captive bullfinch is compared with those of other red pigmented Carduelinae in which male individuals usually lose the red colour in captivity, namely Carpodacus roseus, Carpodacus rubricilloides, Uragus sibiricus, Carduelis cannabina, Carduelis flammea, Loxia curvirostra and Pinicola enucleator
The chemical structure of the pigments in Ara macao plumage,
No full textParrots (Psittaciformes) harbor unusually bright, non-carotenoid, feather pigments. We successfully extracted and purified a sufficient quantity of pigment from the red plumage of the Scarlet Macaw (Ara macao) for a partial chemical analysis. The extracts were analyzed by HPLC coupled with UV-VIS and mass spectroscopy before and after total hydrogenation. We found at least four pigment components. We propose a linear polyenal structure comparable with the molecules tetradecahexenal, hexadecaheptenal, octadecaoctenal and eicosanonenal
- …
