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In common with other hindered structures containing two aromatic rings linked by a short tether, diarylamines may exhibit atropisomerism (chirality due to restricted rotation). Previous examples have principally been tertiary amines, especially those with cyclic scaffolds. Little is known of the structural requirement for atropisomerism in structurally simpler secondary and acyclic diarylamines. In this paper we describe a systematic study of a series of acyclic secondary diarylamines, and we quantify the degree of steric hindrance in the ortho positions that is required for atropisomerism to result. Through a detailed experimental and computational analysis, the role of each ortho-substituent on the mechanism and rate of conformational interconversion is rationalised. We also present a simple predictive model for the design of configurationally stable secondary diarylamines.

Nucleophilic vinylic substitution (SNV) by carbon nucleophiles allows the formation of vinylic C−C bonds without transition metal catalysts. In this paper, we show that tethering two alkenes together through a urea linkage can lead to the formation of a diene by an intramolecular SNV reaction. The starting materials are fully substituted N,N’‐diallyl ureas; the reaction proceeds in the presence of base, and entails a cascade of deprotonations, reprotonations, and an SNV reaction of an allylic carbanion on a rare electrophile: a vinylic urea. As a result, two allylic substituents couple to form a diene, despite the fact that neither is activated towards electrophilic attack. The reaction is tolerant of significant steric bulk, and exhibits regioselectivity with unsymmetrical diallyl ureas: β‐substituted allyl groups invariably behave as nucleophiles, while electrophilic behavior may be enforced by the use of an E‐vinylic urea substituent that cannot be deprotonated under the reaction conditions. [ABSTRACT FROM AUTHOR]

In light of impaction, increasing operational costs, and increased competition among institutions in terms of degrees offered as well as marketing dollars to attract prospective students, state-funded institutions are under increasing pressure to maximize operations via increased efficiency in enrollment management efforts. This study analyzes the impact of a limited-scope public-private partnership on various aspects of the enrollment management funnel for a target set of academic programs at the graduate level in a self-supporting college within a state university system.

The selective reduction of an aromatic trifluoromethyl substituent to a difluoromethyl substituent may be achieved by base‐promoted elimination to form a difluoro‐p‐quinomethide which is trapped by an intramolecular nucleophile. High yields are obtained when the nucleophilic trap entails the conformationally favoured cyclisation of an aminoisobutyric acid (Aib) derivative. The resulting cyclised difluoromethyl‐substituted arylimidazolidinone products are readily converted to versatile difluoromethyl‐substituted aldehydes by reduction and hydrolysis. Defluorination is successful on a range of benzenoid (both para and ortho CF3‐substituted) and heterocyclic substrates. Double defluorination may likewise be achieved sequentially, or in a single step, from an Aib dipeptide derivative. [ABSTRACT FROM AUTHOR]

Preterm birth has been associated with altered microstructural properties of the white matter and lower cognitive ability in childhood and adulthood. Due to methodological limitations of the diffusion tensor model, it is not clear whether alterations in myelination or variation in fibre orientation are driving these differences. Novel models applied to multi‐shell diffusion imaging have been used to disentangle these effects, but to date this has not been used to study the preterm brain in adulthood. This study investigated whether novel advanced diffusion MRI metrics such as microscopic anisotropy and orientation dispersion are altered in adults born preterm, and whether this was associated with cognitive performance. Seventy‐two preterm born participants (<37 weeks gestational age) were recruited from a 1982–1984 cohort (33 males, mean age 33.5 ± 1.0 years). Seventy‐two term born (>37 weeks gestational age) controls (34 males, mean age 30.9 ± 4.0 years) were recruited from the general population. Tensor FA was calculated with FSL, while microscopic FA and orientation dispersion entropy (ODE) were estimated using the Spherical Mean Technique (SMT). Estimated Full Scale IQ (FSIQ), Verbal Comprehension Index (VCI) and Perceptual Reasoning Index (PRI) were obtained from the WASI‐II (abbreviated) IQ test. Voxel‐wise comparisons using FSL's tract‐based spatial statistics were performed to test between‐group differences in diffusion MRI metrics as well as within‐group associations of diffusion MRI metrics and IQ outcomes. The preterm group had significantly lower FSIQ, VCI and PRI scores. Preterm subjects demonstrated widespread decreases in ODE reflecting increased fibre dispersion, but no differences in microscopic FA. Tensor FA was increased in a small area in the anterior corona radiata. Lower FA values in the preterm population were associated with lower FSIQ and PRI scores. An increase in fibre dispersion in white matter and lower IQ scores after preterm birth exist in adulthood. Advanced diffusion MRI metrics such as the orientation dispersion entropy can be used to monitor white matter alterations across the lifespan in preterm born individuals. Although not significantly different between preterm and term groups, tensor FA values in the preterm group were associated with cognitive outcome. [ABSTRACT FROM AUTHOR]

Quaternary amino acids, in which the [alpha]-carbon that bears the amino and carboxyl groups also carries two carbon substituents, have an important role as modifiers of peptide conformation and bioactivity and as precursors of medicinally important compounds.sup.1,2. In contrast to enantioselective alkylation at this [alpha]-carbon, for which there are several methods.sup.3-8, general enantioselective introduction of an aryl substituent at the [alpha]-carbon is synthetically challenging.sup.9. Nonetheless, the resultant [alpha]-aryl amino acids and their derivatives are valuable precursors to bioactive molecules.sup.10,11. Here we describe the synthesis of quaternary [alpha]-aryl amino acids from enantiopure amino acid precursors by [alpha]-arylation without loss of stereochemical integrity. Our approach relies on the temporary formation of a second stereogenic centre in an N'-arylurea adduct.sup.12 of an imidazolidinone derivative.sup.6 of the precursor amino acid, and uses readily available enantiopure amino acids both as a precursor and as a source of asymmetry. It avoids the use of valuable transition metals, and enables arylation with electron-rich, electron-poor and heterocyclic substituents. Either enantiomer of the product can be formed from a single amino acid precursor. The method is practical and scalable, and provides the opportunity to produce [alpha]-arylated quaternary amino acids in multi-gram quantities.This approach introduces an aryl substituent to the [alpha]-carbon of amino acids without a transition-metal catalyst, and uses the inherent chirality of the amino acid itself as the source of asymmetry., Author(s): Daniel J. Leonard [sup.1] , John W. Ward [sup.1] , Jonathan Clayden [sup.1] Author Affiliations:(1) School of Chemistry, University of Bristol, Bristol, UKMain Among the most practical and widely [...]