Current Organic Chemistry, Volume 6, No. 8, 2002
Contents
Ionic Activation of Tin Hydirdes Pp.665-693
Ikuya
Shibata and Akio Baba
The Reaction of Nitrones with Organometallic
Compounds:Scope, Limitations and Synthetic Applications Pp.695-713
Marco
Lombardo and Claudio Trombini
Indium-Mediated Organic Reactions in Aqueous
Media Pp.715-737
Ae
Nim Pae, Yong Seo Cho
Organometallic Derivatives of
Phosphorus-containing Dendrimers. Synthesis, Properties and Applications in
Catalysis. Pp.739-774
Anne-Marie
Caminade, Valérie Maraval, Régis Laurent,Jean-Pierre Majoral
Abstracts
[Back to top] Ionic Activation of Tin Hydirdes
Ikuya
Shibata and Akio Baba
Organotin hydrides
are advantageous reducing agents in terms of their facile availability,
moderate stability and reactivity. In most cases, the dehalogenation of organic
halides by Bu3SnH has taken place under radical conditions.
In contrast, ionic reactions have been conventionally performed by using MeOH
solvent, silica-gel, high pressure, palladium and Lewis acid catalysts. These
ionic reactions have accomplished mild conditions, and high chemo-, regio- and
stereoselectivites have been obtained, however,the ionic reactions have not
received much attention. Another characteristic feature of tin hydrides is that
active metal hydrides have been prepared to induce selective reductions where
tin hydrides are efficient precursors of active metal species. Moreover, we
have developed novel type of tin hydrides by modifying tin center by
introducing ligands and halogen substituents such as Bu3SnH-Ligand,
Bu2SnClH-HMPA, Bu2SnFHHMPA,
Bu2SnIH-LiI and Bu2SnIH-MgBr2.
Noteworthy is their ionic reduction modes that are markedly different from
those of the original Bu3SnH reduction using radical conditions. This
paper summarizes the ionic tin hydride reductions for representative
functionalities such as aldehydes, ketones, epoxides, imines, unsaturated
carbonyls and alkynes. Initially, the control of reducing ability has been
performed by various ionic activation of tin hydrides. In particular, tin
hydride complexes have achieved the chemo- and stereoselective reductions of
carbonyl groups. In the reduction of epoxides, imines and unsaturated carbonyl
compounds, the increased nucleophilicity of the Sn-halogen bond in halogenotin
hydride complexes have played an very important role for high chemo- and
refgioselective reactions. In ionic hydrostannation of alkynes, regio- and stereoselectivities
are summarized for representative substrates. Particularly, the first a-
stannylation of simple aliphatic alkynes could be achieved with an ate type of
tin hydride ate complex.
[Back to top] The Reaction of Nitrones with Organometallic
Compounds:Scope, Limitations and Synthetic Applications
Marco
Lombardo and Claudio Trombini
Synthetic organic
chemists have widely exploited nitrones for the last 50 years as precious
substrates for the assembly of complex nitrogen containing frameworks through
inter and intramolecular 1,3-dipolar cycloadditions. In the last decade the
interest for nitrones was further on increased by a second opportunity, offered
by the nucleophilic addition of organometallic reagents to give
N,N-disubstituted hydroxylamines.
Grignard, lithium
reagents and allylic zinc derivatives react very efficiently with nitrones in a
wide temperature range; both the reaction rate and the stereochemical outcome
of the process can be significantly modified by the addition of
nitrone-chelating Lewis acids. The allylation of nitrones is also carried out
under Sakurai conditions in the presence of trimethylsilyltriflate, and
different results are obtained using allylic silanes or stannanes. Homoallylic
hydroxylamines, generated by the allylation of nitrones, are exploited in
5-exo-trig iodocyclizations to give 5-iodomethyl isoxazolidines, useful
precursors of hydroxylated acyclic and cyclic amino compounds. Enolates and
silyl enol ethers under Mukayama conditions are also investigated. In
particular, 2-trimethylsilyloxyfuran reacts with nitrones, in the presence of
nitrone activators, to give 3-substituted
tetrahydrofuro[2,3-d]isoxazol-5(2H)-ones, easily transformed into a variety of
polyhydroxylated piperidine and indolizidine azasugars. The most recent
solutions to achieve the control of stereochemistry in nucleophilic additions
to nitrones will be examined.
[Back to top] Indium-Mediated Organic Reactions in Aqueous
Media
Ae
Nim Pae, Yong Seo Cho
This review summarizes recent developments that have been reported on organic reactions using indium metal (or salts) in aqueous media. These organic reactions include the carbon-carbon bond formation such as Barbier-type reactions and aldol reactions, reduction, reactions using indium salts in aqueous media, and their synthetic applications.
[Back to top] Organometallic Derivatives of Phosphorus-containing
Dendrimers. Synthesis, Properties and Applications in Catalysis.
Anne-Marie
Caminade, Valérie Maraval, Régis Laurent,Jean-Pierre Majoral
Dendrimers constitute a new class of macromolecules having a hyperbranched and perfectly defined structure. The attractive beauty of these nanosized compounds induces since ten years an exponential development of the number of publications devoted to this topic. Most dendrimers are purely organic compounds, but heteroatom-containing dendrimers also play a role in the development of this field. Among them, dendrimers having phosphorus derivatives, either at each branching point or only in part of the structure (either on the surface, or at the core, or at special places within the structure), occupy a special place. Indeed, the well-known ability of phosphorus derivatives, especially phosphines, to react with organometallic compounds is also applicable to dendritic derivatives of phosphorus. This particular aspect of phosphorus dendrimers, which undergoes a significant development since 5 years, is the subject of this review. The organometallic derivatives can be grafted either to the surface of the dendrimer, or at its core, or throughout the structure, or only at particular places within the structure. Direct phosphorus-metal linkages, but also phosphorus-metal linkages through one atom will be considered. Most of these macromolecules were synthesized for studying their catalytic properties; this important application is emphasized at the end of this review.