Dearomatization of Naphthalene:  Novel Stereoselective Cyclization Reactions Promoted by Osmium(II)

Abstract

A series of Michael acceptors has been combined with the Os(II) eta(2)-naphthalene complex (1) to form stable 1H-naphthalenium species. Under acidic conditions, these complexes undergo ring closure at C2 to form the phenanthrenone core. In contrast, the corresponding 1-methylnaphthalene complex (15) upon addition of MVK at C8 undergoes ring closure at C5 to form a bridged tricyclic complex (18). Michael addition of MVK to the naphthalene complex (1) followed by deprotonation, an inter-ring linkage isomerization, and ring closure forms a 9-methylphenalene complex (21). In all cases, the organic cyclization products may be decomplexed by heating with silver triflate and isolated in moderate yield.

Highly Functionalized Piperidine Generation via Pyridine Repolarization and Hyper-Distorted Allyl Complexes of {TpW(NO)(PMe₃)}

“…The anodic peak potential (E p,a = +0.47 V @100 mV/s; NHE) of 2 is between those of the neutral  2 -pyridine (0.00 V) and  2 -pyridinium complexes (+0.83 V). 4 The X-ray structure of 2 (Scheme 2) depicts the major coordination diastereomer present in solution, 6 in which C4 is adjacent to the PMe 3 ligand.…”

“…Deprotonation of 3H with 2,6-di-tertbutylpyridine (DTBP) in the presence of acetic anhydride results in the acetylpyridinum complex, 4. The initial coordination diastereomer ratio (cdr = 4:1) 5 is improved to >10:1 upon heating (55 °C for 5.5 h), 6 and 4 was ultimately isolated in 94% yield (cdr >10:1). 9 This complex shows a CO stretching feature at 1733 cm -1 (IR), and CO and CN bond lengths of 1.19 and 1.41 Å (X-ray), respectively, consistent with an acetylpyridinium species (resonance form a in Figure 1).…”

“…Nicotine, 1 epibatidine, 2 unconjugated alkenes (~5-6 ppm) due to an anisotropic effect. 5,6 The 1 H chemical shift for H2 is largely unaffected by aromaticity, as it is a typical chemical shift for aldimines.…”

“…This strategy has been utilized in the very concise synthesis of strychnine and the strychnos alkyloids. 43,44 substituted pyridines, allows for their η 6 coordination. 52 Also, precoordination of In general, these expectations held true for many coordinated arenes and resulted in the synthesis of some fairly complicated isolated organic compounds.…”

“…As pyridine does not have substituents to influence binding mode or reactivity, we hoped to gain a greater understanding of the fundamental chemistry of the metal-heterocycle system, elaborate additional possible synthetic pathways available to pyridine, and develop methodologies for the synthesis of new classes of piperidine compounds that its substituted forms do not have access to. We rationalized that the first step to reasonably investigating the fundamental influence the metal plays on the ligand would begin with isolating the complexed conjugate acids of pyridine of synthetically useful scales and then using that (6) Over the past two decades, our group has sought to develop new methods of functionalizing aromatic molecules. 1,2 Our approach exploits the ability of certain π-basic transition metal complexes to bind aromatic molecules through two carbons, thereby localizing the remaining uncoordinated π-system.…”