ABSTRACT
Vinylboronic esters and allylboronic esters are well known to afford olefins by protodeboronation, and therefore homoallenylboronic esters should be similarly available as precursors for 1,3-dienes, but this strategy has not been well explored due to the limited availability of homoallenylboronic esters. Here, we describe a versatile synthesis of homoallenylboronic esters via lithiation-borylation and subsequent 1,2-rearrangement. The resulting homoallenylboronic esters were successfully converted into Z- and E-1,3-dienes by protodeboronation using Bu4NF and B(C6F5)3/PhOH, respectively.
Subject(s)
Esters , Polyenes , AlkenesABSTRACT
Single-crystalline organic semiconductors exhibiting band transport have opened new possibilities for the utilization of efficient charge carrier conduction in organic electronic devices. The epitaxial growth of molecular materials is a promising route for the realization of well-crystallized organic semiconductor p-n junctions for optoelectronic applications enhanced by the improved charge carrier mobility. In this study, the formation of a high-quality crystalline interface upon "quasi-homoepitaxial" growth of bis(trifluoromethyl)dimethylrubrene (fmRub) on the single-crystal surface of rubrene was revealed by using out-of-plane and grazing-incidence X-ray diffraction techniques. Ultraviolet photoelectron spectroscopy results indicated abrupt electronic energy levels and the occurrence of band bending across this quasi-homoepitaxial interface. This study verifies that the minimization of the lattice mismatch enhances the crystalline qualities at the heterojunctions even for van der Waals molecular condensates, potentially opening an untested route for the realization of high-mobility organic semiconductor optoelectronics.
ABSTRACT
A quantitative approach for the development of halogen-bonding-driven anion-binding catalysts was studied using 4-substituted perfluorinated iodobenzene. 19 F NMR titrations were used to determine the binding constants K for chloride, and their catalytic activities were evaluated in the allylation reaction of a N-activated pyridine. We discovered that the log K and product yields were linearly correlated, and that they were dependent on the Hammett substituent parameter, σmeta (r2 =0.99). This linear correlation provided a quantitative predictive model for both the binding constant and the reaction yield. Concomitantly, this efficiently permitted the development of a highly active anion-binding catalyst, namely 4-CNC6 F4 I (K=489±5â M-1 ). Additionally, the catalytic activity of 4-CNC6 F4 I was established in the allylation and crotylation of N-activated isoquinolines (7 examples). Overall, this approach highlights the value of quantitative analysis by exploring experimentally informed correlations in the development of halogen bond donor catalysts.
ABSTRACT
A chiral Brønsted acid containing two different acidic sites, chiral carboxylic acid-monophosphoric acid 1a, was designed to be a new and effective concept in catalytic asymmetric hetero-Diels-Alder reactions of azopyridinecarboxylate with amidodienes. The multipoint hydrogen-bonding interactions among the carboxylic acid, monophosphoric acid, azopyridinecarboxylate, and amidodiene achieved high catalytic and chiral efficiency, producing substituted 1,2,3,6-tetrahydropyridazines with excellent stereocontrol in a single step. This constitutes the first example of regio-, diastereo-, and enantioselective azo-hetero-Diels-Alder reactions by chiral Brønsted acid catalysis.
ABSTRACT
BBr3-chiral phosphoric acid complexes are highly effective and practical Lewis acid-assisted Brønsted acid (LBA) catalysts for promoting the enantioselective Diels-Alder (DA) reaction of α-substituted acroleins and α-CF3 acrylate. In particular, the DA reaction of α-substituted acroleins with 1,2-dihydropyridines gave the corresponding optically active isoquinuclidines with high enantioselectivities. Moreover, transformations to the key intermediates of indole alkaloids, catharanthine and allocatharanthine, are demonstrated.
ABSTRACT
Selective Michael reaction of organolithium reagents to supersilyl methacrylate is reported. The method was able to control a single and double Michael addition. The successful termination of the process using the supersilyl protecting group allows for the controlled, chemoselective, and diastereoselective Michael reaction.
Subject(s)
Lithium/chemistry , Methacrylates/chemistry , Organometallic Compounds/chemistry , Organosilicon Compounds/chemistry , Chemistry Techniques, Synthetic , Crystallography, X-Ray , Indicators and Reagents , Methacrylates/chemical synthesis , Models, Molecular , Organometallic Compounds/chemical synthesis , Organosilicon Compounds/chemical synthesis , StereoisomerismABSTRACT
The first example of intermolecular/intramolecular sequential aldol reaction of disilyl enol ethers is described. This strategy enables the formation of five-, six-, and seven-membered ring products. Four or more contiguous stereogenic centers are created with high levels of relative stereochemical control.
Subject(s)
Aldehydes/chemistry , Ethers/chemistry , Ketones/chemical synthesis , Ketones/chemistry , Molecular StructureABSTRACT
A catalytic enantioselective three-component Mannich-type reaction of alkenyl trichloroacetates, ethyl glyoxalate, and aniline derivatives was achieved using an (S)-BINOL-derived chiral tin dibromide possessing a 4-trifluoromethylphenyl group at the 3- and 3'-positions as the chiral precatalyst in the presence of sodium ethoxide, sodium iodide, and ethanol. Optically active beta-amino ketones with up to 98% ee were syn-selectively obtained in high yields even from imines possessing a polar amino group under the influence of the in situ generated chiral tin bromide ethoxide.
