The identification
of two nickel(II) precatalysts for the preparation
of 2-substituted 1,3-dienes by a Kumada cross-coupling between vinyl
magnesium bromide and vinyl phosphates is described. This is noteworthy
as engaging only one vinyl derivative in a transition-metal-catalyzed
cross-coupling reaction is already reputedly challenging. Salient
features of this method are its operational simplicity, the mild reaction
conditions, the low catalyst loadings, the short reaction times, its
scalability, and the use of stoichiometric quantities of each coupling
partner. The tolerance of the two nickel catalysts to an important
number of reactive functional groups and their compatibility with
structurally complex molecular architectures has been extensively
delineated. A Negishi variant of the reaction has been developed for
even more sensitive organic functions such as ester or nitrile. Several
other conjugated 1,3-dienes with various substitution patterns have
been prepared by combining commercial alkenyl Grignard reagents and/or
readily available alkenyl enol phosphates. Proper choice of the nickel
catalyst and the reaction temperature gave access to a variety of
different olefin isomers with high levels of stereocontrol. Overall,
this approach affords conjugated dienes that would not be accessible
otherwise and therefore provides a valuable complement to existing
methods.
An atypical guanine exchange factor, Dock2 is specifically expressed in hematopoietic cells and regulates activation and migration of immune cells through activating Ras-related C3 botulinum toxin substrate (Rac). Dock2 was shown to be critical in the development of various inflammatory diseases, including allergic diseases, HIV infection, and graft rejection in organ transplantation. DOCK2 mutation in infants was recently identified to be associated with T and B cell combined immunodeficiency. Furthermore, Dock2 is involved in host protection during enteric bacterial infection and is also associated with the proliferation of cancer cells. It was also shown that patients with digestive tract cancer had high frequency mutation of DOCK2. This review summarizes the latest research progresses on the role of Dock2 for the development of various inflammatory diseases and cancers, and discusses the potential application of Dock2 modulators for patient treatment.
A chiral Lewis acid-promoted cyclopropanation using a phenyliodonium ylide as the carbene precursor was developed. An EPR spectroscopy study supported a stepwise biradical mechanism.
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