Scalable Total Syntheses and Structure-Activity Relationships of Haouamines A, B, and Their Derivatives as Stable Formate Salts.

Haouamines A, B, and their derivatives were synthesized via Suzuki-Miyaura coupling and three key cyclization reactions as follows: the newly developed palladium(0)-catalyzed arylative cyclization of phenylalanine-derived alkyne-aldehydes with 2-bromoarylboronic acid (an "anti-Wacker"-type cyclization); BF ⋅OEt -promoted Friedel-Crafts-type cyclization of symmetrical electron-rich aromatic rings adjacent to a tertiary allylic alcohol leading to the indeno-tetrahydropyridine skeleton; and (cyanomethyl)trimethylphosphonium iodide-mediated macrocyclization of amino alcohols to afford aza-paracyclophane precursors. The palladium-catalyzed reduction of mono- and di-triflate intermediates in the later stages enabled the alteration of both the position and number of hydroxyl groups on the C-ring. The instability of haouamine B was dramatically improved by salt formation with formic acid.