1,2-Amino Alcohols via Cr/Photoredox Dual-Catalyzed Addition of α-Amino Carbanion Equivalents to Carbonyls

Herein, we report the synthesis of protected 1,2-amino alcohols starting from carbonyl compounds and α-silyl amines. The reaction is enabled by a Cr/photoredox dual catalytic system that allows the in situ generation of α-amino carbanion equivalents which act as nucleophiles. The unique nature of this reaction was demonstrated through the aminoalkylation of ketones and an acyl silane, classes of electrophiles that were previously unreactive toward addition of alkyl-Cr reagents. Overall, this reaction broadens the scope of Cr-mediated carbonyl alkylations and discloses an underexplored retrosynthetic strategy for the synthesis of 1,2-amino alcohols.

2-{[(4-Methoxyphenyl)dimethylsilyl]methyl}isoindoline-1,3-dione

In the course of our studies of silicon-containing anti­cancer compounds, the title compound, C₁₈H₁₉NO₃Si, was synthesized. The mol­ecular geometry including bond distances and angles involving the Si atoms are typical. Torsion angles associated with the isoindoline ring and the silyl group [C—N—C_methyl­ene—Si = 90.5 (2) and −93.1 (2)°] indicate that there is no inter­action between the O and Si atoms despite silicon’s high affinity for oxygen.

2-[3-(Methyldiphenylsilyl)propyl]isoindoline-1,3-dione

In the title compound, C₂₄H₂₃NO₂Si, the dihedral angle between the planes of the phenyl rings attached to the Si atom is 80.78 (10)°. In the crystal, the mol­ecules form sheets lying perpendicular to [101] via C—H⋯O inter­actions. These sheets are stacked and linked in a three-dimensional framework by additional C—H⋯O inter­actions in the [10] direction.

2-[2-(Trimethylsilyl)ethyl]isoindoline-1,3-dione

In the course of our studies of silicon-containing anti­cancer compounds, the title compound, C₁₃H₁₇NO₂Si, was synthesized. The geometrical parameters including the geometry about the Si atom are typical. The mol­ecules form dimers via a weak C—H⋯O inter­action described by the graph set R₂²(10). The dimers are assembled in rows stacked in the crystallographic b-axis direction via π–π inter­actions with a 3.332 (3) Å separation between the rows.

(Dimethylaminomethyl)trifluorosilane, Me2NCH2SiF3—A Model for the α-Effect in Aminomethylsilanes

F3SiCH2NMe2 was prepared as a model for the investigation of the nature of the alpha-effect in alpha-aminosilanes, by fluorination of Cl3SiCH2NMe2 with SbF3. Under less mild conditions Si--C bond cleavage was also observed, leading to the double adduct F4Si(Me2NCH2SiF3)2, which was characterised by a crystal structure analysis showing that the central SiF4 unit is connected to Me2NCH2SiF3 via SiN dative bonds and FSi contacts. F3SiCH2NMe2 was characterised by multinuclear NMR spectroscopy (1H, 13C, 15N, 19F and 29Si), gas-phase IR spectroscopy and mass spectrometry. It is a dimer in the crystal (X-ray diffraction, crystal grown in situ), held together by two Si--N dative bonds. In solution and in the gas phase the compound is monomeric. The structure of the free molecule, determined by gas-phase electron diffraction, showed that, in contrast to former postulates, there are no attractive SiN interactions. Ab initio calculations have been carried out to explain the nature of the bonding. F3SiCH2NMe2 has an extremely flat bending potential for the Si-C-N angle; the high degree of charge transfer from the Si to the N atoms which occurs upon closing the Si-C-N angle is in the opposite direction to that expected for a dative bond. The topology of the electron density of F3SiCH2NMe2 was analysed. Solvent simulation calculations have shown virtually no structural dependence on the medium surrounding the molecule. The earlier postulate of Si-->N dative bonds in SiCN systems is discussed critically in light of the new results.