Molybdenum-Promoted Dearomatization of Pyridines

Abstract

A second-row transition metal complex {MoTp­(NO)­(DMAP)} (DMAP = 4-(dimethylamino)­pyridine; Tp = tris­(pyrazolyl)­borate) is shown to form dihapto-coordinate complexes with a range of substituted pyridines bearing both electron-withdrawing and electron-donating substituents. Subsequent reactivity of the pyridine ligand is demonstrated by protonation and nucleophilic addition reactions.

The Tungsten-Promoted Synthesis of Piperidyl-Modified erythro-Methylphenidate Derivatives

“…As with the mesylated analogs, the Reformatsky reaction occurred with low stereoselectivity. Two examples of the parent methyl phenyl acetate THP ( 21-Ac and 21-Ts ) were prepared and are included in Figure for comparison. , …”

“…Previous studies exploring the tungsten-promoted dearomatization of pyridine utilized an acetyl protecting group (PG = Ac; Figure ), where the corresponding pyridinium complex could be prepared in up to a 10:1 cdr mixture. − The N -acetyl-2-ethyl acetate-1,2-dihydropyridine complex 2D was synthesized via a Reformatsky reaction between the corresponding pyridinium complex ( 1 ), methyl bromoacetate (MBA), and zinc . Owing to the position of the metal, the addition cleanly occurs at C2, with no sign of competing C4 addition . It was postulated that a similar strategy could be utilized to install the methyl phenylacetate moiety to the pyridinium core.…”

“…Two examples of the parent methyl phenyl acetate THP (21-Ac and 21-Ts) were prepared and are included in Figure 7 for comparison. 25,26 Hydrogenation of the THP to Piperidine. As a demonstration of the ability to generate the corresponding piperidines from THPs such as those reported in Figure 7, THP 21-Ms was reduced to its saturated analogue (26) through hydrogenation.…”

Synthesis of 1-Azatriene Complexes of Tungsten: Metal-Promoted Ring-Opening of Dihydropyridine

“…This observation is consistent with metal-backbonding into the azadiene π-system. 24 We anticipate that the driving force behind this reaction is the generation of a 1-azatriene ligand, which is an excellent πacceptor for the π-basic [W] fragment. 16 For example, DFT calculations indicate that the conversion of 6D to 16D is −2.8 kcal/mol.…”

“…Bond lengths for the azatriene ligand are unremarkable, being largely in agreement with the crystal data of organic analogues − but with a slight shortening (∼0.02 Å) of the C4–C5 and C2–C3 bonds. This observation is consistent with metal-backbonding into the azadiene π-system …”