10.1021/ol015743j
The study presents a novel and efficient chiral auxiliary-based method for the synthesis of C-glycosylated amino acids. The key step involves a 1,3-dipolar cycloaddition of a chiral glycine equivalent and carbohydrate building blocks, leading to the formation of products with high regio- and diastereoselectivity. The chiral auxiliary, derived from (?)-menthone or (+)-menthone, allows for the synthesis of corresponding diastereomers. The method is designed to meet criteria for an easy and broadly applicable approach to a variety of products with different configurations, as well as orthogonal protecting group strategies. The study also explores the reductive cleavage of the N?O bond using SmI2, which is compatible with the protecting groups on the glycosidic moiety. The approach is demonstrated to be broadly applicable with various aglycosidic building blocks, and it is shown that a chiral glycine equivalent is necessary for the diastereomeric purity of the cycloaddition products. The research was financially supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
10.1016/S0040-4039(02)00597-X
The research focuses on the improved addition of phenyllithium (PhLi) to hindered ketones using non-polar media at room temperature. The study was conducted on six hindered ketones: (?)-fenchone, (?)-menthone, (+)-camphor, 3,3,5-trimethylcyclohexanone, 3,3,5,5-tetramethylcyclohexanone, and 2,4-dimethylpentan-3-one. The researchers aimed to enhance the low reactivity of these ketones towards PhLi, which traditionally yields modest results when performed in ethers like diethyl ether or THF. The experiments involved dissolving the ketones in a non-polar solvent, such as toluene or a toluene-diethyl ether mixture, and then slowly adding commercial PhLi via syringe. The mixtures were stirred at room temperature for 2 to 4 hours. The results showed significant improvements in yield compared to traditional methods, with the addition occurring in a stereospecific manner, favoring the less-hindered side. The configuration of the adducts was established using 13C NMR according to literature methods. This approach was found to be more efficient, cost-effective, and easier, offering a significant advantage for the synthesis of chiral inducers.
10.1055/s-1988-27647
The research aims to synthesize chiral allenes from naturally occurring chiral ketones such as camphor or menthone, in order to obtain enantiomerically pure, sterically hindered allenes for investigating chiral induction in cycloadditions. The researchers used various chemical reactions and reagents, including the addition of dihalocarbene to double bonds, Wittig reactions, and reactions with lithium dimethylcuprate. They also employed techniques like 13C-NMR investigation and phase-transfer catalysis. The study found that some reactions were not trivial due to the difficulty in preparing exo-methylene compounds and the tendency of allenes to rearrange under certain conditions.
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