Carbocation Catalysis: Oxa‐Diels–Alder Reactions of Unactivated Aldehydes and Simple Dienes

Abstract

The versatility of the trityl cation (TrBF4) as a highly efficient Lewis acid organocatalyst is demonstrated in the oxa‐Diels–Alder reaction of various unactivated aromatic and aliphatic aldehydes and simple unactivated dienes, such as isoprene and 2,3‐dimethylbutadiene. The transformation proceeds smoothly to give 3,6‐dihydropyrane adducts in high to moderate yields with catalyst loadings down to 1.0 mol‐% under mild reaction conditions. In contrast to most previously reported strategies, this protocol does not require substrate functional group activation, neither by electron‐deficient aldehydes (2‐oxo aldehydes) or electron‐rich dienes (methoxy or amino‐butadiene).

Ligand-Directed Conformational Control over Porphyrinic Zirconium Metal–Organic Frameworks for Size-Selective Catalysis

“…To evaluate the catalytic performance of PCN-625(Fe), we compared its activity with those of other reported catalysts for the cycloaddition between 1c and 2a (Table S11). It was found that PCN-625(Fe) exhibited a performance superior to those of the reported UNLPF-16-Fe III , 52 FeP p−H -HCP, 53 TrBF 4 , 54 [Fe(TPP)]BF 4 , 51,55 Sc-(OPf) 3 , 56 and AlCl 3 , 57 which required higher amounts of catalysts or longer reaction time but afforded lower yields. Meanwhile, due to their similar skeletal structures, its catalytic performance was almost the same as that of PCN-223(Fe).…”

Thieno[2,3-b]thiophene Derivatives as Potential EGFRWT and EGFRT790M Inhibitors with Antioxidant Activities: Microwave-Assisted Synthesis and Quantitative In Vitro and In Silico Studies

“…Cancer is a well-recognized disease with a multifactorial nature that is known for uncontrolled cell growth and abnormal cell spread as well. − It is ranked to be the second cause of death all over the world. , Nowadays, there are various techniques to fight cancer such as chemotherapy, radiotherapy, and/or surgery. − The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase (RTK) that is involved in the development and homeostasis of epithelial tissues. − Moreover, the family of EGFR has a vital role in cell signaling through overexpression which is linked to the progress of various human solid malignancies, especially breast cancers and non-small-cell lung cancers. − The use of EGFR inhibitors to block EGFR-mediated signaling pathways is a common approach for the treatment of several malignancies. − There are three generations of EGFR-tyrosine kinase inhibitors available: the first one includes reversible EGFR inhibitors (erlotinib and gefitinib); the second generation includes irreversible EGFR blockers (afatinib and dacomitinib); and the third one includes a wild-type-sparing, irreversible EGFR inhibitor (osimertinib). The fourth generation inhibitors (which include EAI04518 and other non-covalent inhibitors) are now in preclinical testing. , In addition, the EGFR is well established as a biomarker in the case of resistant cancers, as its secondary mutations have been observed to occur under treatment components …”

“… 11 − 14 Moreover, the family of EGFR has a vital role in cell signaling through overexpression which is linked to the progress of various human solid malignancies, especially breast cancers and non-small-cell lung cancers. 15 − 18 The use of EGFR inhibitors to block EGFR-mediated signaling pathways is a common approach for the treatment of several malignancies. 17 − 19 There are three generations of EGFR-tyrosine kinase inhibitors available: the first one includes reversible EGFR inhibitors (erlotinib and gefitinib); the second generation includes irreversible EGFR blockers (afatinib and dacomitinib); and the third one includes a wild-type-sparing, irreversible EGFR inhibitor (osimertinib).…”

Cooperativity in Diiron(III)porphyrin Dication Diradical-Catalyzed Oxa-Diels–Alder Reactions: Spectroscopic and Mechanistic Insights

“…Heteroatoms at the β-position of the aryl aldehydes can greatly promote the reactivity of the substrates. Franzen and co-workers reported a carbocation-catalyzed ODA reaction . The possible role of counteranions toward the efficiency of this reaction and spectroscopic insights of the reaction has yet not been explored.…”