Intramolecular reaction

About: Intramolecular reaction is a research topic. Over the lifetime, 5015 publications have been published within this topic receiving 138213 citations.

Investigations of glycosylation reactions with 2-N-acetyl-2N,3O-oxazolidinone-protected glucosamine donors.

Abstract: NIS/AgOTf-promoted glycosylations with ethyl 2,3-N,O-carbonyl-2-deoxy-1-thio-beta-D-glucopyranoside donors can be performed with either alpha- or beta-selectivity by tuning the reaction conditions. Small amounts of AgOTf (0.1 equiv) and short reaction times give beta-selectivity, whereas 0.4 equiv of AgOTf and prolonged reaction times afford alpha-linked products. NMR-monitored glycosylation and anomerization experiments show initial formation of exclusively the beta-linkage, which anomerizes, through an intramolecular mechanism involving an endocyclic C-O bond cleavage, to the alpha-linkage.

General access to the vinca and tacaman alkaloids using a Rh(II)-catalyzed cyclization/cycloaddition cascade.

Abstract: The total synthesis of several members of the vinca and tacaman classes of indole alkaloids has been accomplished. The central step in the synthesis consists of an intramolecular [3+2]-cycloaddition reaction of an α-diazo indoloamide which delivers the pentacyclic skeleton of the natural product in excellent yield. The acid lability of the oxabicyclic structure was exploited to establish the trans-D/E ring fusion of (±)-3H-epivincamine (3). Finally, a base induced keto-amide ring contraction was utilized to generate the E-ring of the natural product. A variation of the cascade sequence of reactions used to synthesize (±)-3H-epivincamine was also employed for the synthesis of the tacaman alkaloids (±)-tacamonine and (±)-apotacamine.

Syntheses of (±)-α- and (±)- γ- Lycorane via a Stereocontrolled Organopalladium Route

Abstract: Total syntheses of (+/-)-alpha-and (+/-)-gamma-lycorane are described. The key steps in the syntheses are the stereocontrolled palladium-catalyzed intramolecular 1,4-chloroamidation of 12 to 13 and the subsequent anti-stereoselective copper-catalyzed S(N)2' reaction of allylic chloride 13 with [3,4-(methylenedioxy)phenyl]magnesium bromide to give 14. Hexahydroindole 14 has the required relative stereochemistry between carbons 3a, 7, and 7a for alpha-lycorane (1a) and was transformed to the latter via 15 and 16. The epimeric gamma-lycorane (2) was obtained by performing the Bischler-Napieralski cyclization on 14, which led to a highly stereoselective isomerization to give exclusively 17. Compound 17 was subsequently transformed to 2. The overall yield from ester 8 to (+/-)-alpha- and (+/-)-gamma-lycorane was 40 and 36%, respectively.