Investigations in the dipiperidyl series

Chiral N-Heterocyclic Carbene Ligands Derived from 2,2‘-Bipiperidine and Partially Reduced Biisoquinoline: Rhodium and Iridium Complexes in Asymmetric Catalysis

“…Separation of meso and racemic forms via the corresponding hydrochloride salt was first reported in the literature in 1971. 13 Numerous attempts of separation, in our hands, however were completely unsuccessful. This difficulty prompted us to search for alternative methods.…”

“…All six complexes are very soluble in dichloromethane and THF and not soluble in saturated hydrocarbons. Their identities are confirmed by elemental analysis and 1 H NMR, 13 C NMR, and mass spectroscopy. The complexes are air stable in the solid state and for several days in solution.…”

“…Both enantimericaly pure bpip-bishydrobromide 3 and octahydrobiisoquinoline bishydrobromide 9 reacted easily with triethyl orthoformate, yielding corresponding imidazolinium salts 8 and 10, Scheme 3. The 1 H and 13 C NMR spectra of 8 and 10 are indicative of C 2 -symmetric compounds. For example, compound 10 exhibits a strong singlet at δ 5.41 ppm that is attributable to adjacent protons of two octahydroisoquinoline rings.…”

“…Compound 2: 1 H NMR (D 2 O): δ 3.42 (4H, apparent t, J ) 11.9 Hz); 3.04 (2H, apparent t, J ) 12.9 Hz); 1.88 (6 H, m); 1.55 (6H, m). 13 (RS)-2-((RS)-Piperidin-2-yl)piperidine (4). (RS)-2-((RS)-Piperidin-2-yl)piperidine bishydrobromide (3) (9.88 g, 29.94 mmol) was stirred in CH 2 Cl 2 (50 mL) and 5 M NaOH (50 mL) at room temperature for 1 h. The organic layer was separated and dried over NaOH.…”

“…1 H NMR (CDCl 3 ): δ 3.03 (2H, d, J ) 11.7 Hz); 2.57 (2H, t, J ) 11.7 Hz); 2.33 (2H, d, J ) 9.8 Hz); 1.77 (2H, d, J ) 10.8 Hz); 1.55 (4H, t, J ) 12.7 Hz); 1.43-1.17 (8H, m). 13 9-(2-Isopropyl-5-menthylcyclohexyloxy)decahydro-8a,9a-diaza-9-phosphafluorene-9-sulfide (bpip-P(S)-l-menthyl 5, 6). (RS)-2-((RS)-Piperidin-2-yl)piperidine (4) (4.88 g, 28.99 mmol) was dissolved in 100 mL of CH 2 Cl 2 in a flame-dried flask.…”