New Polycyclic Diamine Scaffolds from Dimerization of 3-Alkyl-1,4-dihydropyridines in Acidic Medium

Baldwin and Whitehead's Manzamine Alkaloids Biosynthesis Hypothesis Involves a Finely Tuned Reactivity of Acrolein: Automated Extraction of Reactivity Patterns from LC-MS2 Data

Inspired by the multicomponent reaction-type scenario involving fatty dialdehydes, a nitrogen source, and acrolein, as a key C3 unit, put forward by Baldwin and Whitehead to explain the formation of manzamine-type alkaloids, 96 multicomponent reactions were designed, and their analytical readouts were deconvoluted using a herein-provided chemoinformatic workflow. This strategy pinpointed relevant conditions tuning the reactivity of acrolein to fulfill Baldwin and Whitehead's manzamine alkaloids biosynthetic hypothesis. This strategy can become part of a general method for the high-content analysis of multicomponent reactions applied to a natural product biosynthetic scenario.

Regiocontrolled Dimerization of Densely Functionalized 1,6-Dihydropyridines for the Biomimetic Synthesis of a Halicyclamine-type Scaffold by Preventing Disproportionation

The biomimetic dimerization of 1,6-dihydropyridines (DHPs) remains a daunting challenge due to competitive disproportionation pathways. Herein we report the regioselective dimerization of densely functionalized 1,6-DHPs that allow direct access to the bis-nitrogen bicyclic scaffold of halicyclamines. Disproportionation triggered by the hydride shift of 1,6-DHP was suppressed by the use of geminal disubstituted substrates. Installation of an electron-withdrawing substituent at the C3 position was demonstrated to be crucial for facilitating biomimetic dimerization under metal-free conditions, with exquisite control of regioselectivity at ambient temperature. Our approach, featuring an appropriately functionalized and substantially stabilized substrate rather than merely adopting the highly reactive and labile hypothetical biosynthetic intermediate, allowed gram-scale and atom-economical synthesis of the bis-nitrogen bicyclic scaffold. Furthermore, conversion of a series of 1,6-DHPs provided mechanistic insights by circumventing the competitive disproportionation reaction. This revealed not only the innate reactivity of the conjugate diene system for [4 + 2] cycloaddition but also the reversibility of the dimerization reaction with multiple cationic intermediates in equilibrium.

Silylation of Pyridine, Picolines, and Quinoline with a Zinc Catalyst

Zn(OTf)2 (OTf- = trifluoromethanesulfonate) catalyzes the silylation of pyridine, 3-picoline, and quinoline to afford the silylated products, where the silyl groups are meta to the nitrogen. The isolated yields of the products range from 41 to 26%. The 2- and 4-picolines yielded the silylmethylpyridines, where the CH3 groups were silylated instead of the ring. The pyridine silylation can occur via two separate pathways, involving either a 1,4- or a 1,2-hydrosilylation of pyridine as the first step. A byproduct of the pyridine silylation is a head-to-tail dimerization of N-silyl-1,4-dihydropyridine to form a diazaditwistane molecule.

Synthesis and reactivity of imide-derived bisvinyl phosphates. Reactivity of 2,6-disubstituted 1,4-dihydropyridines

Symmetrical and unsymmetrical 2,6-disubstituted dihydropyridines were prepared in high yields under mild conditions using the Suzuki and Stille Pd-catalyzed coupling reactions of imide-derived bisvinyl phosphates with a range of aryl, heteroaryl, and alkenyl moieties. The alkylation reaction at C-4 easily afforded original tri- and tetrasubstituted dihydropyridines. Hydrolysis of the latter under acidic condition provided efficiently either open-chain 1,5-diketones or di- or trisubstituted pyridines.

Retracted article: Biogenetic hypothesis and first steps towards a biomimetic synthesis of haouamines

A detailed hypothesis for the biogenesis of haouamines is reported herein, supported by experiments headed towards biomimetic synthesis of these compounds.