The first enantiospecific total synthesis of a C-quaternary voachalotine alkaloid, (+)-dehydrovoachalotine

DDQ catalyzed oxidative lactonization of indole-3-butyric acids

Benzylic C-H bonds next to electron rich aromatic rings are susceptible to 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) promoted functionalization. In this work benzylic carbocations formed in this manner are trapped by a pendant carboxylic acid to form a lactone. Indole-3-butyric acids are especially good substrates for the reaction. The lactonization functions well with catalytic amounts of DDQ combined with MnO2 as the stoichiometric oxidant. This cyclization proceeds with a number of indole-3-butyric acids, and yields were generally good as long as the indole was electron rich and free of bulky substituents near the reacting benzylic carbon. Indole-3-butyric acids functionalized with electron withdrawing groups tend to give more moderate yields. Other aromatic substrates also participate as long as the aromatic ring is functionalized with electron donating groups.

Sarpagine and Related Alkaloids

The sarpagine-related macroline and ajmaline alkaloids share a common biosynthetic origin, and bear important structural similarities, as expected. These indole alkaloids are widely dispersed in 25 plant genera, principally in the family Apocynaceae. Very diverse and interesting biological properties have been reported for this group of natural products. Isolation of new sarpagine-related alkaloids and the asymmetric synthesis of these structurally complex molecules are of paramount importance to the synthetic and medicinal chemists. A total of 115 newly isolated sarpagine-related macroline and ajmaline alkaloids, along with their physicochemical properties have been included in this chapter. A general and efficient strategy for the synthesis of these monomeric alkaloids, as well as bisindoles, has been presented, which involves application of the asymmetric Pictet-Spengler reaction (>98% ee) as a key step because of the ease of scale up of the tetracyclic template. Also included in this chapter are the syntheses of the sarpagine-related alkaloids, published since 2000.

Synthesis of 2-(3'-Indolyl)tetrahydrofurans by oxidative cycloetherification

A series of 2-(3'-indolyl)tetrahydrofurans have been prepared by a DDQ-mediated oxidative cycloetherification process. Performing the reaction under biphasic conditions prevents reductive cleavage of the products by the spent oxidant (DDQH2).

General Approach to the Total Synthesis of Macroline-Related Sarpagine and Ajmaline Alkaloids1

Described in this review is a general and efficient strategy for the synthesis of macroline-related sarpagine and ajmaline alkaloids. The tetracyclic ketone in the parent system, as well as the alkoxy substituted series served as templates for the synthesis of these complex molecules. The palladium-mediated enolate cross coupling process, regiospecific hydroboration, and Tollens reaction are some of the key transformations that have been employed for further functionalization of these templates. Synthetic routes that have been improved, in order to obtain gram quantities of these alkaloids form a part of this review.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

This review covers the literature on simple indole alkaloids and those with a nonrearranged monoterpenoid unit from the beginning up to the end of 2004. Newly isolated alkaloids, structure determinations, total synthesis and biological activities are included.