Catalytic Cyclization of o‐Alkynyl Phenethylamines via Osmacyclopropene Intermediates: Direct Access to Dopaminergic 3‐Benzazepines

Abstract

A novel osmium-catalyzed cyclization of o-alkynyl phenethylamines to give 3-benzazepines is reported. The procedure allows the straightforward preparation of a broad range of dopaminergic 3-benzazepine derivatives. Mechanistic investigations revealed that the process takes place via osmacyclopropene intermediates, which were isolated and characterized by X-ray crystallography.

Catalytic Cyclization of o‐Alkynyl Phenethylamines via Osmacyclopropene Intermediates: Direct Access to Dopaminergic 3‐Benzazepines

“…Intermediate 6 was also isolated and characterized by Xray diffraction analysis. [19] As expected, the addition of KOtBu (1.0 equiv) to solutions of 5 in THF at room temperature led to deprotonation of the metal center and the formation of 6,which was isolated as an orange solid in 88 % yield. Them ost interesting feature is the orientation of the C(2)ÀHb ond, which, in contrast to the structure of 5,p oints away from the cyclopentadienyl ligand.…”

“…The treatment of solutions of 4 in dichloromethane with the substrate (1.1 equiv) at room temperature for 5h led to the osmacyclopropene derivative 5,which was isolated as an offwhite solid in 60 %y ield. TheX-ray crystal structure of 5 [19] proved the formation of the osmacyclopropene moiety,which implies the oxidation of the metal center by two units.Thus,the distribution of ligands around the metal center is that expected for ac yclopentadienyl osmium(IV) species and can be described as af ourlegged-piano-stool geometry,i nw hich the cyclopentadienyl group occupies the three-membered face,a nd the two Catoms of the metallacycle,t he hydride ligand, and the phosphine ligand lie in the plane of the four-membered face. TheO s ÀC(1) and OsÀC(2) bond lengths of 1.941(6) and 2.219 (8) , respectively,c ompare well with those found in other osmacyclopropene compounds [20] and support the double and single character of the bonds.I na greement with this structure,t he 13 C{ 1 H} NMR spectrum contained al owfield C(1) resonance at 207.5 ppm and ah igh-field C(2) resonance at À12.7 ppm.…”

Osmium Complexes With POP Pincer Ligands

“…The ruthenium counterpart of 4, cis-RuCl 2 {κ 1 -S-(DMSO)} 4 (20), has also proved to be a useful starting point to develop the {xant(P i Pr 2 ) 2 }Ru chemistry. Treatment of toluene solutions of 20 with 1 equivalent of xant(P i Pr 2 ) 2 , under reflux, affords RuCl 2 {κ 3 agreement with the tendency of ruthenium to avoid the oxidation state four.…”

“…The scarce development of the pincer-osmium chemistry is probably due to the rooted belief that osmium is not useful in catalysis because it is a reductant and prefers to be coordinatively saturated and forms redox isomers with greater metal-carbon multiplicity [10-13]. However, recent findings have proved that osmium can be a promising alternative to the metals classically used in catalysis [14][15][16][17][18][19][20][21][22][23].The chemistry of the pincer-osmium complexes has been mainly focused on a few PCP derivatives reported by the groups of Gusev [24-28], Jia [29][30][31] and Milstein [32,33] and PNP complexes described by the groups of Caulton [34-37], Gusev [38-41], and Jia [42], along with some CCC [43-46], CCN [47], CNC [48,49], CNN [50-52], CNO [53], and NNN [54-59] species.We synthesized the diphosphines xant(P i Pr 2 ) 2 and dbf(P i Pr 2 ) 2 in 2010 [60], and subsequently started our research program on POP complexes of platinum group metals [3,[60][61][62][63][64][65], including osmium [60,[66][67][68][69][70][71]. In this chapter, we summarize the results obtained for this element until now.…”

“…The scarce development of the pincer-osmium chemistry is probably due to the rooted belief that osmium is not useful in catalysis because it is a reductant and prefers to be coordinatively saturated and forms redox isomers with greater metal-carbon multiplicity [10-13]. However, recent findings have proved that osmium can be a promising alternative to the metals classically used in catalysis [14][15][16][17][18][19][20][21][22][23].…”