Current Organic Chemistry - Volume 19, Issue 14, 2015

This review with 800 references illustrates applications of Suzuki-Miyaura (S.-M.) reactions in the total syntheses of 147 natural products that were made in the period 2010–2013. The review has been organized on the basis of the seven classes of phosphane-based Pd catalysts that have been used in the reported total syntheses. Emphasis has been given to describe and discuss the experimental conditions of the Pd-catalyzed (S.-M.) cross-coupling reactions also outlining the methods used to prepare the reactants. A focus has also been set on the biological and pharmacological properties of the reported natural products as well as on the most significant steps of the reported total syntheses.

1,3-dipolar cycloadditions have been studied extensively for decades. The advantages of this synthetic approach may be increased further by applying microwave irradiation. The substrates for 1,3CA reactions are particularly sensitive to microwave heating due to their dipolar nature. Furthermore, the lack of solvent effects and a catalyst that may be applied in the solid phase make these reactions even more suitable for microwave enhancement. In this review we present the advantages of microwave heating in the synthesis of nitrogen heterocycles through 1,3-dipolar cycloaddition. Although it has been studied for years, this area of synthetic chemistry still requires further elucidation.

Alliin (S-allyl-L-cysteine sulfoxide) and isoalliin (S-1-propenyl-L-cysteine sulfoxide) are major organosufur compounds in Allium species that contain sulfur and carbon stereocenters. Alliin is the precursor of allicin, which is one of the most biologically active molecules in garlic. Isoalliin is the precursor of onion’s lachrymatory factor, and is responsible for the pink discoloration of onion and the green/blue discoloration of garlic. Many synthesis schemes of diastereomers of alliin and isoalliin are discussed in this review. Alliin can be synthesized by not only the classical method of sulfur oxidation using hydrogen peroxide, but also asymmetric sulfur oxidation using tetraisopropyl ortho-titannate or oxygenase. Besides typical method of using allyl bromide and then isomerization by a base catalyzed reaction, isoalliin can also be synthesized by Pd-catalyzed carbon sulfur coupling of (E)-1-bromoprop-1-ene. Fractional crystallization and HPLC have proven to be effective tools in isolation of diasteriomers. Synthesis of the selenium analogue of alliin is also presented in this review.

The explanation for the rate enhancing effect of microwave (MW) irradiation is still the subject of controversy. It is, however, agreed that it may involve the possible role of thermal effects. In this article, our explanation is presented using the example of the direct esterification of a cyclic phosphinic acid, modelling the distribution of the local overheatings by exponential functions for the first time, and taking the effect of the overheatings into consideration by the Arrhenius equation. One of the explanatory models described well the experimental rate enhancement observed for the MW-assisted direct esterification of 1-hydroxy-3-methyl-3- phospholene 1-oxide with butanol.