Synthesis of chiral group 14 hydrides containing a c(,2)-symmetric binaphthyl substituent and their application in stereoselective free radical organic reactions.

摘要

Some reactions of the previously synthesized first chiral tin hydride containing a C₂-symmetric binaphthyl substituent {lcub}(S)-4,5-dihydro-4-methyl-3H-dinaphtho[2,1-c:1 ′,2′-e]stannepin{rcub} are described. The effect of different Lewis acids in some of these reactions was also evaluated. Reduction of racemic 2-phenyl-2-bromo-1-indanone, methyl 2-bromo-2-phenyl propionate, phenyl 2-bromo-2-phenyl propionate and 3-iodo-3-methoxymethyl-2-chromanone afforded low to good yields (18–78%) and low enantioselectivities (0–21%) of 2-phenyl-1-indanone, methyl 2-phenyl propionate, phenyl 2-phenyl propionate and 3-methoxymethyl-2-chromanone, respectively. Hydrostannylation of 1,1- and 1,2-disubstituted olefins (methyl methacrylate, 2-naphthyl methacrylate, N-methacryloyl-2-oxazolidinone, N-methacryloyl pyrrolidine, methyl 2-phenyl acrylate, (E)-cyclohexyl crotonate and methyl cinnamate) afforded the diastereoisomeric adducts in variable yields (9–96%) and low diastereoisomeric ratio (1:1–1.8:1).; Several attempts to synthesize and isolate a new tin hydride containing a C₂-symmetric binaphthyl substituent and two tin-sulfur bonds were ultimately unsuccessful.; The synthesis of two novel germanium hydrides containing a C ₂-symmetric binaphthyl substituent and two germanium-sulfur bonds (4-tert-butyl-3,5-dithia-4-germa-cyclohepta[2,1-a;3,4-a ′]dinaphthalene and 4-tert-butyl-2,6-bis-trimethylsilyl-3,5-dithia-4-germa-cyclohepta[2,1-a;3,4-a ′]dinaphthalene was accomplished. The germanium hydrides are very stable as solids and the X-ray crystal structure of the ortho silylated germanium hydride was obtained. The kinetic constants for hydrogen transfer to a primary alkyl radical were measured by indirect competition methods and were found to be 3.0 × 107 M−1 s−1 for the non-silylated hydride (at 83°C), and 1.4 × 107 M−1 s−1 for the silylated hydride (at 80°C). Reduction of racemic halides 3-iodo-3-methoxymethyl-2-chromanone and methyl 2-bromo-2-phenyl-3,3-dimethylbutanoate with the non-silylated hydride afforded 3-methoxymethyl-2-chromanone and methyl 2-phenyl-3,3-dimethylbutanoate in high yields (79–100%) and low enantioselectivities (20–29%). Hydrogermylation of methyl methacrylate gave a 3:1 ratio of (R,R)/(R,S) adduct. The relative configuration was established by X-ray crystallography of the minor isomer. Reduction of racemic halides 3-iodo-3-methoxymethyl-2-chromanone and methyl 2-bromo-2-phenyl-3,3-dimethylbutanoate with the silylated hydride afforded the reduced products in moderate yields (30–70%) and moderate enantioselectivities (23–59%). Hydrogermylation of methyl methacrylate gave excellent ratios of (R,R)/( R,S) adduct (11:1–25:1) in moderate yields (54–63%). The relative configuration was established by X-ray crystallography of the alcohol obtained by reduction of the major diastereoisomer.