Palladium and Raney Nickel Catalyzed Methanolic Cleavage of Stable Borane−Amine Complexes

Abstract

[figure: see text] Palladium and Raney nickel were found to catalyze the methanolysis of borane-amine adducts. Hence, strongly complexed amines can now be liberated by simple treatment with Pd/C or Raney Ni in methanol. The method is applicable to primary, secondary, tertiary, and aromatic amines, and the mildness of the reaction conditions allows preservation of otherwise labile functional groups.

Highly Diastereoselective Additions to Polyhydroxylated Pyrrolidine Cyclic Imines: Ready Elaboration of Aza‐Sugar Scaffolds To Create Diverse Carbohydrate‐Processing Enzyme Probes

“…Reduction of imide 13 was achieved by reaction with borane/dimethylsulfide complex yielding the corresponding borazine as the sole product, which was cleaved to yield N-benzylpyrrolidine by heating overnight in methanol at 40 8C (100 % yield from 13); this borazinecleavage method provides a convenient alternative to other methods. [25] Removal of the N-benzyl group by catalytic hydrogenation over palladium-on-carbon yielded the iminothreitol 9 in 43 % yield over four steps from tartaric acid, identical in all respects to that synthesized from 6.…”

“…The aqueous layers were extracted with CHCl 3 (2 Â 10 mL) and the combined organic layers dried (Na 2 SO 4 ), filtered and concentrated under reduced pressure to yield a yellow oily solid (277 mg). This crude product was purified by flash column chromatography on silica gel (EtOAc/cyclohexane 1: 19 3.92 (m, 1 H; NCH 2 CHOSi), 6.84 (m, 2 H; 2 of C 6 H 4 ), 7.14 (m, 2 H; 2 of C 6 H 4 ); 13 C NMR (100 MHz, CDCl 3 , HSQC, DEPT): d À 5.0, À 4.7, À 4.7, À 4.6 (4 q, 4 Â SiCH 3 ), 17.8, 17.9 (2 s, 2 Â SiC(CH 3 ) 3 ), 25.7, 25.9 (2 q, 2 Â SiC(CH 3 ) 3 ), 39.1 (t, C 6 H 4 CH 2 ), 53.9 (t, NCH 2 ), 55.3 (q, OCH 3 ii) Reverse mode of addition: According to method described for 29 a using a THF solution of imine (6 mL 1b-Hex-5-enyl-2,3-O-isopropylidene-1,4-dideoxy-1,4-iminoerythritol (30 g) i) Imine formation: DBU (0.11 mL, 111 mg, 0.73 mmol, 1.3 equiv) was added under Ar to a solution of 21 (100 mg, 0.56 mmol) in dry THF (6 mL). The reaction mixture was stirred, whereupon the white salt DBU ¥ HCl precipitated.…”

Scope and Selectivity of Heterogeneous Rh0‐Catalyzed Tandem Dehydrocoupling/Hydrogenation Using Me2NH·BH3 as a Stoichiometric H2 Source

“…For example, Couturier and co-workers have reported the Pd-catalyzed methanolysis of Me 3 N·BH 3 and tBuNH 2 ·BH 3 , [10] and their utilization as hydrogen transfer reagents for the hydrogenation of a range of organic compounds, such as nitrobenzenes to anilines (Scheme 2). [11] Scheme 2.…”

Synthesis of Cortistatins A, J, K and L

“…41 Regioselective reductive cleavage of the allylic C−O bond of the resulting acetate occurred in the presence of lithium borohydride (excess) and tetrakis(triphenylphosphine)-palladium (0.2 equiv). 42 This afforded the dimethylamino diene 34 in complex with borane; decomplexation was achieved by treatment of this intermediate with Raney nickel in methanol, 43 providing the free amine as a pale yellow solid (90% yield after chromatographic purification over Davisil® silica gel). Silyl ether cleavage (tetra-n-butylammonium fluoride, 87% yield) and oxidation (Dess−Martin periodinane, 90%), then completed the route to the 17-keto cortistatin K precursor (35), also obtained as a pale yellow solid.…”