Triple bond alumination: a general synthesis of aromatic and heteroaromatic organoaluminum compounds – TriBAl

Classical synthetic routes for the preparation of organoaluminum reagents are so far rather limited, and usually require the preparation and transformation of a first organometallic compound (organolithium or magnesium) or the metalation a precursor, leading to organoaluminum species with no or limited reactivity, especially in solvents able to neutralize their Lewis acidity. The aim of this study was the discovery of new synthetic methods for the preparation of organoaluminum that would overcome these limitations, eading to reactive species in non-coordinating solvent

During this project, a new acces to aluminated heterocycles has been developed. Unexpectedly, the mechanistic investigation of the rection led to the discovery of a new king of reactivity between aluminum acetylides and diazo compounds, leading to a novel class of reagents: silylated diazoalkynes. The reactivity of these novel chemical entities has been investigated, leading to the unprecedented preparation of silylated diazoalkynes are their use for the synthesis of propargyl bis(silanes).
The preparation of organoaluminum compounds using flow chemistry techniques has also been developed.

This work has confirmed the interest of exploring the unique reactivity of organoaluminum reagents. They led to unexpected results, such as the reaction of aluminum alkynides with TMS diazomethane, and open new perspective for the preparation of non symmetrical bis-silyl dérivatives.
The preparation of aluminum acetylides using flow chemistry is also promising for further developements in this field.

The reaction of dimethylalkynylaluminum reagents with trimethylsilyldiazomethane : original reactivity leading to new ??silylated alkynylhydrazones R. Kumar, S. Turcaud, L. Micouin, Org. Lett. 2014, 16, 6192-6195.

Continuous Flow Synthesis of Dimethylalkynylaluminum Reagents, R. Piccardi, A. Coffinet, E. Benedetti, S. Turcaud, L. Micouin, Synthesis 2016, in press

Rhodium(II)-Alkynyl Carbenoids Insertion into Si-H bonds : An entry to propargylic geminal bis(silanes). T. Courant, R. Kumar, S. Turcaud, L. Micouin, Org. Lett. 2016, Under revision

Chapitre d'ouvrage
The Chemistry of Alkynylaluminum Species, R. Piccardi, O. Jackowski, L. Micouin, in The chemistry of organoaluminum compounds, Patai, Ed by I. Marek, Z. Rappoport and L. Micouin, in press.

Book
The chemistry of organoaluminum compounds, Patai, Ed by I. Marek, Z. Rappoport and L. Micouin, 2016 John Wiley & Sons, Ltd., in press

Conference
«Triple bond alumination: a general synthesis of aromatic and heteroaromatic organoaluminum compounds«, colloque ANR mi-parcours, Grenoble, 15-16 janvier 2015

Communications (posters)

New ??silyl-Diazo and hydrazo compounds from TMS diazomethane and alkynylaluminum reagents. T. Courant, R. Kumar, L. Micouin XIV ICSN Symposium, Gif-sur Yvette, 18-19 juillet 2015

Rhodium(II)-Alkynyl Carbenoids Insertion into Si-H bonds : An entry to propargylic geminal bis(silanes). T. Courant, R. Kumar, S. Turcaud, L. Micouin, FJS 2016, Tokyo, 15-18 mai 2016.

The main objective of this work is to develop new routes to organoaluminic aromatic and heterocyclic compounds and study their reactivity. As demonstrated by recent developments, there is a growing interest in the field of organoaluminum chemistry, and aromatic or heteroaromatic aluminum compounds should be potentially attractive as synthetic building blocks. However, aromatic and heterocyclic aluminum chemistry has not been well developed, probably because of the lack of versatile methods for their preparation.
A conventional preparative method for (het)aromatic organoaluminum compounds is the transmetalation of the corresponding lithium or magnesium derivatives with various aluminum(III) sources. This pathway has some serious limitations:
-The functional group tolerance of the carbon-aluminum bond is lost if one starts from the corresponding lithiated or magnesiated derivatives.
-The transmetalation procedure generates salts as side products. These salts have been reported to strongly affect the reactivity of the final organoaluminum reagent and the enantioselectivity of asymmetric processes.
-This procedure is very often conducted in ethereal solvents, known to strongly decrease the Lewis acidity of organoaluminum reagents, and therefore to affect their reactivity.
The deprotonation of aromatic rings is another very convenient way to prepare organoaluminum compounds. This method however leads to compounds with diminished Lewis acidity (ate complexes, generally in THF, or aluminum amides). As a consequence, the (het)aromatic reagents have to be transmetalated before further reaction. A directing group is also required for the metalation step.
A third method involves activation of aluminum by a small amount of metallic salts enabling the preparation of aromatic or allenic aluminum sesquihalides in a very efficient manner by oxidative addition. This method however delivers a mixture of organometallic species.
In this project, we propose to define a new general route to neutral functionalized aluminated heterocycles using a metalative cyclization on a carbon-carbon triple bond as a key step. We also want to establish a new general route to neutral functionalized aromatic or heteroaromatic oragnaoaluminum reagents using a selective carbo- or heteroalumination of an in–situ generated aryne or hetaryne
The reactivity of all these aluminic species, generated in non-coordinating solvents, under "salt free" conditions, will then be investigated.