Asymmetric bromolactonizations of alkynes are possible using a desymmetrization approach. The commercially available catalyst (DHQD)2PHAL promotes these cyclizations in combination with cheap NBS as a bromine source to give bromoenol lactones in high yield and with high enantioselectivity. The bromoenol lactone products, containing a tetrasubstituted alkene and a quaternary stereocenter, are valuable building blocks for synthetic chemistry.

The DNA G-quadruplex-binding porphyrin TMPyP4·Cu was found to form efficient hybrid catalysts for DNA-based asymmetric catalysis when bound to DNA G-quadruplexes. Nucleobase substitution experiments using human telomere-derived G-quadruplex sequences suggest binding of the porphyrin on the 3'-face.

Halocyclization reactions such as halolactonization are powerful synthetic methods for the functionalization of alkenes and alkynes. However, asymmetric versions were thought of as difficult reactions and only recently have new asymmetric, organocatalytic halocyclization methods been reported. Herein, we examine a specific strategy for asymmetric halocyclization reactions, desymmetrizing cyclizations, and highlight recent contributions in this area.

γ‐Alkynoic acids readily undergo iodolactonization to give iodoenol lactones. Using commercially available (DHQD)2PHAL this transformation can be rendered asymmetric. In desymmetrization reactions of dialkynoic acids, good to very good enantioselectivities can be observed. Alternatively, kinetic resolution of already chiral, racemic γ‐alkynoic acids can be carried out. The products of these iodolactonizations, iodoenol lactones, are suitable substrates for Palladium catalyzed cross‐couplings. Negishi‐ as well as Sonogashira couplings can be carried out and allow the efficient synthesis of highly substituted enol lactones.

The cinchona alkaloid dimer (DHQD) PHAL has been shown to be a broadly applicable catalyst for asymmetric halogenations. However, this catalyst does not have to be dimeric and a class of monomeric quinidine and quinine-derived catalysts was prepared, often showing superior selectivity in bromolactonisations of terminal alkynoic acids. Mechanistic investigations show that these organocatalysts act as host molecules that can bind carboxylic acid-based substrates as guests with substantial binding constants. Based on these findings, it is proposed that this class of catalysts is bifunctional in nature activating the halogenating agent as well as the nucleophile in electrophilic halogenation reactions.