A facile access to optically active 2‐indolyl‐1‐nitro derivatives, which can be easily transformed into highly valuable compounds such as tryptamines and 1,2,3,4‐tetrahydro‐β‐carbolines, is provided by the first catalytic enantioselective Friedel–Crafts alkylation of indoles with nitroalkenes (see scheme; e.g. R1=R2=H, R3=Ph).
In
this contribution, we provide an overview of the main avenues
that have emerged in gold coordination chemistry during the last years.
The unique properties of gold have motivated research in gold chemistry,
and especially regarding the properties and applications of gold compounds
in catalysis, medicine, and materials chemistry. The advances in the
synthesis and knowledge of gold coordination compounds have been possible
with the design of novel ligands becoming relevant motifs that have
allowed the preparation of elusive complexes in this area of research.
Strong donor ligands with easily modulable electronic and steric properties,
such as stable singlet carbenes or cyclometalated ligands, have been
decisive in the stabilization of gold(0) species, gold fluoride complexes,
gold hydrides, unprecedented π complexes, or cluster derivatives.
These new ligands have been important not only from the fundamental
structure and bonding studies but also for the synthesis of sophisticated
catalysts to improve activity and selectivity of organic transformations.
Moreover, they have enabled the facile oxidative addition from gold(I)
to gold(III) and the design of a plethora of complexes with specific
properties.
In this review, recent advances in catalytic asymmetric hydrophosphonylation of aldehydes and imines are discussed. We also summarize several proposed mechanisms for the different possibilities of asymmetric induction and the application of this catalytic methodology to the enantioselective synthesis of α‐amino and α‐hydroxy phosphonates. A variety of metal‐based chiral catalysts as well as several organic catalysts have been exploited as suitable systems for the preparation of enantiomerically pure phosphonates. The recent evolution and future trends of those and other catalytic systems are described.
A review of the general volcano-stratigraphy and geochronology of La Gomera, one of the lesser known Canary Islands, has led to the establishment of a new evolutionary model. The oldest edifice corresponds to the submarine stage built up between 20 and 15 Ma. The construction of the Submarine Edifice was followed by an important break in the activity (about 4 Ma) and deep erosion of the edifice. About 10.5 Ma ago, the main present-day edifice (the Old Edifice 10.5-6.4 Ma) emerged, which was also submarine in its initial phases. Two different main stages are distinguishable. The first stage was represented by a large, some 22 km wide basaltic shield volcano (the Lower Old Edifice). Several lateral collapse events (Tazo and San Marcos avalanches) occurred during this time and were responsible for the removal of an important part of its northern flank. In the second growth stage (the Upper Old Edifice), the activity migrated southwards. A 25-km wide composite volcano arose covering part of the remaining earlier shield volcano. The felsic (trachytic to phonolitic) activity occurring in two separate episodes formed a significant component of this composite volcano. Finally, one more recent large edifice (the Young Edifice) built up from 5.7 to 4 Ma. The lava flows of this younger edifice covered completely the centre and the south of the island and filled deep ravines in the north. More evolved magmas, including significant felsic magmas (the third and last felsic episode), occurred in this phase of activity.The growth of La Gomera was long-lasting, separated by an important gap in the activity in the Middle Miocene, with no Quaternary activity at all. At the same time on Tenerife (the nearest island east of La Gomera), three large edifices grew separately: Roque del Conde, Anaga and Teno (initially three separated islands). From the available data, it is inferred that the subaerial activity started earlier in the Roque del Conde Edifice, then on La Gomera and later in Teno in the NW and Anaga in NE of Tenerife, which is the youngest of all these edifices. These facts, together with the irregular general progress of the volcanic activity, support more complex views of the genesis for the Canary Islands than the simple hotspot model.
(1S,2R)-1-Aminoindan-2-ol-derived thioureas behave as efficient H-bonding organocatalysts for the nucleophilic conjugate addition of formaldehyde hydrazones to beta,gamma-unsaturated alpha-keto esters as enoate surrogates, affording the corresponding adducts in good yields and enantioselectivities.
Ein leichter Zugang zu optisch aktiven 2‐Indolyl‐1‐nitro‐Derivaten, die problemlos in wertvolle Tryptamine und 1,2,3,4‐Tetrahydro‐β‐carboline umgewandelt werden können, eröffnet sich durch die erste katalytische enantioselektive Friedel‐Crafts‐Alkylierung von Indolen mit Nitroalkenen (siehe Schema; z. B. R1=R2=H, R3=Ph).
The enantioselective alkylation of α,β-unsaturated aldehydes with stabilized carbocations as electrophiles via the activation as dienamine intermediates is described. This unique application of dienamine catalysis allows for the first enantioselective γ-alkylation of linear α,β-unsubstituted enals.
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