Rearrangement of a Transient Gold Vinylidene into Gold Carbenes.

The gold acetylide complex 20 endowed with a biaryl backbone provides opportunities for a study on the formation and fate of gold vinylidenes. Although the formyl group in 20 is not sufficiently electrophilic to get attacked by the acetylide in proximity, its activation with TBSOTf (TBSOTf=tert-butyldimethylsilyl trifluoromethanesulfonate) at low temperature triggered instantaneous formation of a gold vinylidene (21). This metastable species evolved into the cationic gold carbene complex 22 bearing a phenanthrene unit and a hydroxyl group at the aurated center; the recorded data suggest that this product might be better viewed as an acylgold species protonated by triflic acid. The use of [Me3 O⋅BF4 ] as the activating agent led to formation of the analogous Fischer-type carbene 24, whereas replacement of gold by the [CpRu(PPh3 )2 ]+ fragment allowed the ruthenium vinylidene 27 to be isolated, which closely resembles the proposed gold intermediate 21. The starting gold complex 20, the derived products 22 and 24, as well as vinylidene 27 were characterized by X-ray diffraction.

Tandem Addition of Phosphite Nucleophiles Across Unsaturated Nitrogen-Containing Systems: Mechanistic Insights on Regioselectivity.

The addition of phosphite nucleophiles across linear unsaturated imines is a powerful and atom-economical methodology for the synthesis of aminophosphonates. These products are of interest from both a biological and a synthetic point of view: they act as amino acid transition state analogs and Horner-Wadsworth-Emmons reagents, respectively. In this work the reaction between dialkyl trimethylsilyl phosphites and α,ß,γ,δ-diunsaturated imines was evaluated as a continuation of our previous efforts in the field. As such, the first conjugate 1,6-addition of a phosphite nucleophile across a linear unsaturated N-containing system is reported herein. Theoretical calculations were performed to rationalize the observed regioselectivites and to shed light on the proposed mechanism.

3-Imidoallenylphosphonates: In Situ Formation and ß-Alkoxylation.

3-Imidoallenylphosphonates, allenes bearing both an electron-withdrawing and -donating group, were isolated for the first time. An alkoxy substituent was introduced into these unprecedented intermediates in a one-pot approach, yielding ß-functionalized aminophosphonates in excellent yields and short reaction times. The mechanistic insights gained are important additions to the domain of allene chemistry. Addition of biologically important molecules, including monoglycerides, amino acids, and nucleosides, proves the general applicability of the developed method.

Gold superacid-catalyzed preparation of benzo[c]thiophenes.

A three-step synthesis of benzo[c]thiophenes is presented in which the key transformation is the gold-catalyzed 5-exo-dig migratory cycloisomerization of a diallyl thioacetal. It was shown that a small amount of in situ generated HAuCl4 from AuCl3 is the active catalytic species. A mechanism was proposed.

Preparation of phosphines through C-P bond formation.

Phosphines are an important class of ligands in the field of metal-catalysis. This has spurred the development of new routes toward functionalized phosphines. Some of the most important C-P bond formation strategies were reviewed and organized according to the hybridization of carbon in the newly formed C-P bond.

Preparation of tetrasubstituted 3-phosphonopyrroles through hydroamination: scope and limitations.

Phosphonylated pyrroles were obtained by a ZnCl2-catalyzed 5-exo-dig hydroamination of propargylic enamines. These starting compounds were obtained in two steps from commercially available ß-ketophosphonates. The method tolerates a wide variety of substituents at the 1,2- and 5-position of the pyrrole, while further derivatization allows for the introduction of substituents at the 4-position via lithiation or halogenation.

Synthetic entry into 1-phosphono-3-azabicyclo[3.1.0]hexanes.

3-Azabicyclo[3.1.0]hex-2-en-1-yl phosphonates were prepared in a five-step reaction route from ß-ketophosphonates. The key steps in this sequence are an atom-transfer radical cyclization and an unforeseen lithium-halogen exchange with n-BuLi. The cyclization reaction proceeds with excellent diastereoselectivity. The resulting cyclic imines were reduced, and 3-azabicyclo[3.1.0]hexan-1-yl phosphonates were obtained.