Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Phospholane Boranes, Sulfides and Oxides

Reaction of meso-115 with a chiral lithium amide at very low temperature (100 °C) furnished, after addition of several electrophiles, the chiral products 116 in good yields and optical purities (Table 5.19). [Pg.276]

Only the diastereomer maintaining the syn arrangement of the three phenyl rings was formed, in eomparable yields and rather similar enantioselectivities of around 85% ee irrespeetive of the electrophile employed. The optical purity of [Pg.276]

Some of the enantiopure phospholane oxides 116 were used for further transformations. For example, they could be isomerised by treatment with base for several hours in a protic solvent to afford 117 or subjected to a second deprotonation to produce 118 as a single isomer. Attempts to prepare Z)w(phospholanes) by double nucleophilic attack of the anions derived from 116 were unsuccessful. Some of the phospholane oxides were reduced with tri-chlorosilane/pyridine to afford the free phospholane with retention of configuration. The same strategy was applied to 1-phenylphospholane oxide but low yields of racemic products were obtained. This suggests that substrate 115 is probably a special case due to the formation of a more stable benzylic carbanion.  [Pg.277]

In this case the carbanion was quenched with dry ice in order to prepare the a-carboxylated phospholane borane 123. This compound was obtained as a [Pg.277]

The enantioselective deprotonation of 128 and oxidative addition of the carbanion with Cu(II) afforded TangPhos disulfide as a mixture of diaster-eomers where the chiral C2-symmetric product was the major compound (66% de, 95% ee). A single recrystallisation afforded the desired optically pure TangPhos sulfide in 20% yield. The desulfuration was performed with hexa-chlorodisilane to yield the very air-sensitive Tangphos diphosphine in 88% yield. The synthesis of a family of phospholane-oxazoline ligands started with the preparation of carboxylic acid 129 by the proeedure in 40% yield after recrystallisation. The crude product was obtained in relatively low optical [Pg.279]


See other pages where Phospholane Boranes, Sulfides and Oxides is mentioned: [Pg.274]   


SEARCH



Borane oxidation

Borane sulfides

Boranes oxidation

Oxides and sulfides 9, 11

Oxides sulfides

Phospholane oxides

Phospholanes

Sulfides oxidation

© 2024 chempedia.info