Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines

• Jian-bo Xie,
• Jian Luo,
• Timothy R. Winn,
• David B. Cordes and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 746–751, doi:10.3762/bjoc.10.69

• conducted in simple and easy ways without any column chromatographic purification, which defines the GAP (group-assisted purification) chemistry concept. It was found that the optically pure isomer (dr > 99:1) can be readily obtained by washing the crude mixture of the asymmetric borylation reaction with

• recrystallization (Scheme 1). Recently, our group has established a concept called GAP (group-assisted purification) chemistry for greener synthesis [22][23][24][25]. This concept describes a process where special functional groups are attached onto reaction substrates, facilitating purification of crude products

Synthesis of chiral N-phosphinyl α-imino esters and their application in asymmetric synthesis of α-amino esters by reduction

• Yiwen Xiong,
• Haibo Mei,
• Lingmin Wu,
• Jianlin Han,
• Yi Pan and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 653–659, doi:10.3762/bjoc.10.57

• chromatography and recrystallization. The chiral phosphinyl auxiliary could be easily cleaved under acidic conditions. Keywords: α-amino ester; α-imino ester; group-assisted purification; phosphinyl auxiliary; reduction; Introduction α-Imino esters play a very important role in the field of imine chemistry [1

• starting materials, an easy modification of the auxiliary and a highly diastereoselective control. Furthermore, the phosphonyl auxiliaries can do favor in the final purification, and it did not need any column chromatography or recrystallization, which was summarized as GAP (group assisted purification

• GAP (group-assisted purification) was introduced into the reaction [49][50][51]. In five cases (Table 4, entries 1, 3–5 and 11), the final purified products were obtained by just washing with hexane, and no column chromatography or recrystallization was needed. Determination of the absolute