Enantiocontrolled Synthesis of a Tetracyclic Aminal Corresponding to the Core Subunit of Diazonamide A
摘要:
A chiral benzylic ether serves as an auxiliary for oxindole carboxylation (dr 5.2:1.0) that sets C-10 configuration in a potential diazonamide precursor. The chiral substituent allows diastereomer separation and departs during a subsequent acid-catalyzed ring closure to form a tetracyclic aminal. With suitable N-protection, crystallization affords the aminal with 9899% ee.
Enantiocontrolled Synthesis of a Tetracyclic Aminal Corresponding to the Core Subunit of Diazonamide A
摘要:
A chiral benzylic ether serves as an auxiliary for oxindole carboxylation (dr 5.2:1.0) that sets C-10 configuration in a potential diazonamide precursor. The chiral substituent allows diastereomer separation and departs during a subsequent acid-catalyzed ring closure to form a tetracyclic aminal. With suitable N-protection, crystallization affords the aminal with 9899% ee.
enantioselective addition to aldehydes by using a titanium(IV) catalyst derived from a H8‐binaphthol derivative in the presence of [Ti(OiPr)4] and MgBr2. A range of functionalities, including olefin, chlorine atoms, protected alcohols, amides, and cyano groups, are tolerated in the present reaction, providing the corresponding functionalized alcohols in high yields and enantioselectivities (see scheme)
在[Ti(O i Pr)4 ]和MgBr 2存在下,使用衍生自H 8-联萘酚衍生物的钛(IV)催化剂,可以将官能化的烷基卤化锌用于醛的对映选择性加成反应。在本反应中可以耐受多种官能团,包括烯烃,氯原子,受保护的醇,酰胺和氰基,从而以高收率和对映选择性提供相应的官能化醇(参见方案)。
Copper(I)‐Catalyzed Enantioconvergent Borylation of Racemic Benzyl Chlorides Enabled by Quadrant‐by‐Quadrant Structure Modification of Chiral Bisphosphine Ligands
作者:Hiroaki Iwamoto、Kohei Endo、Yu Ozawa、Yuta Watanabe、Koji Kubota、Tsuneo Imamoto、Hajime Ito
DOI:10.1002/anie.201906011
日期:2019.8.5
The first copper(I)‐catalyzed enantioselective borylation of racemic benzyl chlorides has been realized by a quadrant‐by‐quadrant structure modulation of QuinoxP*‐type bisphosphine ligands. This reaction converts racemic mixtures of secondary benzyl chlorides into the corresponding chiral benzylboronates with high enantioselectivity (up to 92 % ee). The results of mechanistic studies suggest the formation
of aldehyde by the catalysis of a chiraltitaniumcomplex derived from DTBP-H8-BINOL. The reaction is performed with good stoichiometry [1.5 equiv each of Grignard reagents and ClTi(OiPr)3] at a low catalyst loading (2 mol %), affording a variety of chiral secondary alcohols in high enantioselectivity and yields and, hence, realizing an asymmetric version of the Grignard reaction in an indirect manner
由格氏试剂和ClTi(O i Pr)3原位生成的烷基钛试剂可通过催化衍生自DTBP-H 8 -BINOL的手性钛配合物用于醛的对映选择性烷基化反应,而无需进一步操作。该反应以良好的化学计量[1.5当量的格氏试剂和ClTi(O i Pr)3 ]在低催化剂负载量(2mol%)下进行,从而以高对映选择性和收率提供了多种手性仲醇,因此,间接实现格氏反应的不对称形式。
Catalytic Enantioselective Alkylation and Arylation of Aldehydes by Using Grignard Reagents
the resulting mixed titanium reagents undergo addition to aldehydes with high enantioselectivities (typically >90% ee) and high yields. The method is applicable to various combination of aldehydes (R 1 CHO; R 1 = aryl, heteroaryl, 1-alkenyl, and alkyl) and Grignard reagents (R 2 MgX; R 2 = primary alkyl and aryl). Thus, a variety of enantiomerically enriched secondary alcohols (R 1 CH*(OH)R 2 ) can