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31.
The Negishi cross-coupling reaction of vinylic- and aryltellurides with heteroarylzinc chlorides catalyzed by PdCl2/CuI is described. This cross-coupling reaction is general and permits the formation of a new sp2-sp2 carbon bond in good yields and high stereoselectivity. 相似文献
32.
The bicyclic and tricyclic meso-N-(methylsulfonyl)dicarboximides 1a–f are converted enantioselectively to isopropyl [(sulfonamido)carbonyl]-carboxylates 2a–f by diisopropoxytitanium TADDOLate (75–92% yield; see Scheme 3). The enantiomer ratios of the products are between 86:14 and 97:3, and recrystallization from CH2Cl2/hexane leads to enantiomerically pure sulfonamido esters 2 (Scheme 3). The enantioselectivity shows a linear relationship with the enantiomer excess of the TADDOL employed (Fig.3). Reduction of the ester and carboxamide groups (LiAlH4) and additional reductive cleavage of the sulfonamido group (Red-Al) in the products 2 of imide-ring opening gives hydroxy-sulfonamides 3 and amino alcohols 4 , respectively (Scheme 4). The absolute configuration of the sulfonamido esters 2 is determined by chemical correlation (with 2a,b ; Scheme 6), by the X-ray analysis of the camphanate of 3e (Fig. 1), and by comparative 19F-NMR analysis of the Mosher esters of the hydroxy-sulfonamides 3 (Table 1). A general proposal for the assignment of the absolute configuration of primary alcohols and amines of Formula HXCH2CHR1R2, X = O, NH, is suggested (see 11 in Table 1). It follows from the assignment of configuration of 2 that the Re carbonyl group of the original imide 1 is converted to an isopropyl ester group. This result is compatible with a rule previously put forward for the stereochemical course of reactions involving titanium TADDOLate activated chelating electrophiles ( 12 in Scheme 7). A tentative mechanistic model is proposed ( 13 and 14 in Scheme 7). 相似文献
33.
Michel Lebœuf Diego Cortes Reynald Hocquemiller André Cavé Angèle Chiaroni Claude Riche 《Tetrahedron》1982,38(19):2889-2896
The structure of guoregine, a new isoquinoline alkaloid from , Annonaceae, has been deduced by spectral analysis and confirmed by an X-ray structure determination. It is the first member of a new class of cularine-related alkaloids (α--dimetyltetradehydrocularines). 相似文献
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Carlos Humberto Valencia-Llano Diego Lpez-Tenorio Marcela Saavedra Paula A. Zapata Carlos David Grande-Tovar 《Molecules (Basel, Switzerland)》2022,27(18)
Autologous bone is the gold standard in regeneration processes. However, there is an endless search for alternative materials in bone regeneration. Xenografts can act as bone substitutes given the difficulty of obtaining bone tissue from patients and before the limitations in the availability of homologous tissue donors. Bone neoformation was studied in critical-size defects created in the parietal bone of 40 adult male Wistar rats, implanted with xenografts composed of particulate bovine hydroxyapatite (HA) and with blocks of bovine hydroxyapatite (HA) and Collagen, which introduces crystallinity to the materials. The Fourier-transform infrared spectroscopy (FTIR) analysis demonstrated the carbonate and phosphate groups of the hydroxyapatite and the amide groups of the collagen structure, while the thermal transitions for HA and HA/collagen composites established mainly dehydration endothermal processes, which increased (from 79 °C to 83 °C) for F2 due to the collagen presence. The xenograft’s X-ray powder diffraction (XRD) analysis also revealed the bovine HA crystalline structure, with a prominent peak centered at 32°. We observed macroporosity and mesoporosity in the xenografts from the morphology studies with heterogeneous distribution. The two xenografts induced neoformation in defects of critical size. Histological, histochemical, and scanning electron microscopy (SEM) analyses were performed 30, 60, and 90 days after implantation. The empty defects showed signs of neoformation lower than 30% in the three periods, while the defects implanted with the material showed partial regeneration. InterOss Collagen material temporarily induced osteon formation during the healing process. The results presented here are promising for bone regeneration, demonstrating a beneficial impact in the biomedical field. 相似文献
35.
Developing more efficient catalytic processes using abundant and low toxicity transition metals is key to enable their mainstream use in synthetic chemistry. We have rationally designed a new Mn(i)-catalyst for hydroarylation reactions that displays much improved catalytic activity over the commonly used MnBr(CO)5. Our catalyst, MnBr(CO)3(MeCN)2, avoids the formation of the off-cycle manganacycle-(CO)4 species responsible for low catalyst activity, allowing near room temperature hydroarylation of alkenes and alkynes with broad functional group tolerance including late stage functionalisation and diversification of bioactive molecules.A Mn(i)-catalyst for hydroarylation reactions, MnBr(CO)3(MeCN)2, avoids the formation of the off-cycle manganacycle-(CO)4 species responsible for low catalyst activity typical of MnBr(CO)5, leading to mild and broad scope hydroarylation. 相似文献
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Dr. David Martínez-López Eduardo Santamaría-Aranda Dr. Marco Marazzi Dr. Cristina García-Iriepa Dr. Diego Sampedro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(13):4420-4429
Donor–acceptor Stenhouse adducts (DASAs) are playing an outstanding role as innovative and versatile photoswitches. Until now, all the efforts have been spent on modifying the donor and acceptor moieties to modulate the absorption energy and improve the cyclization and reversion kinetics. However, there is a strong dependence on specific structural modifications and a lack of predictive behavior, mostly owing to the complex photoswitching mechanism. Here, by means of a combined experimental and theoretical study, the effect of chemical modification of the π-bridge linking the donor and acceptor moieties is systematically explored, revealing the significant impact on the absorption, photocyclization, and relative stability of the open form. In particular, a position along the π-bridge is found to be the most suited to redshift the absorption while preserving the cyclization. However, thermal back-reaction to the initial isomer is blocked. These effects are explained in terms of an increased acceptor capability offered by the π-bridge substituent that can be modulated. This strategy opens the path toward derivatives with infra-red absorption and a potential anchoring point for further functionalization. 相似文献
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