Reaction of allylic tin reagents with nitrogen heteroaromatics activated by alkyl chloroformates: regioselective synthesis of .alpha.-allylated 1,2-dihydropyridines and change of the regioselectivity depending on methyl substituents at the allylic moiety

Abstract

ChemInform Abstract The N-(alkoxycarbonyl)pyridinium chlorides (I), formed in situ from pyridine and alkyl chloroformates, react with allyltributyltin (II) to yield the 2-substituted 1,2-dihydropyridines (III) with a high regioselectivity, along with minor amounts of the 4-substituted 1,4-dihydropyridines (IV). The same α-regioselectivity is observed in the reaction of the m-substituted pyridines (V) with methyl chloroformate (VI) and (II) as outlined in the reaction scheme. No regioselectivity is found in the reaction of (Ia) with methallyl-and crotyltributyltin (IX), producing the compounds (X) and (XI). Further reactions are describted in the original paper.

Insertion of Pyridine into the Calcium Allyl Bond: Regioselective 1,4‐Dihydropyridine Formation and CH Bond Activation

“…[2a, 4] Grignard [5] or organotin [6] reagents mainly add to give 2-substituted DHPs. 1,4-DHPs with substituents in the 4-position can be obtained with ill-defined organotitanium reagents, [7] lithium dialkylcuprates, [8] and mixtures of Grignard reagents or zinc organyls with cuprous salts.…”

Dearomatization Strategies in the Synthesis of Complex Natural Products

“…[57] According to this concept, Schmitz and co-workers proposed a biosynthesis of (À)-longithorone A (44) involving consecutive inter-and intramolecular Diels-Alder cycloadditions. [58] A few years later, Shair and co-workers disclosed an elegant biomimetic synthesis of (À)-longithorone A (44) involving an intermolecular Diels-Alder cycloaddition between [12]paracyclophanes 168 and 169 promoted by a Lewis acid to generate cyclohexene derivative 170 in 70 % yield (d.r. 1:1.4; Scheme 22).…”

“…[11] Synthesis of the azabicyclo-[2.2.2]octane (isoquinuclidine) core of 22 commenced with the alkylative dearomatization at the C2 position of an acylpyridinium derived from pyridine 23 to introduce an allyl side chain. [12] Further desilylation generated allenoate intermediate 24 which participated in intramolecular [4+2] cycloaddition to furnish the nirurine core structure in two steps.…”

Desaromatisierungsstrategien in der Synthese strukturell komplexer Naturstoffe

“…Anfang der 1990er Jahre im Zusammenhang mit ihrer Totalsynthese des pentacyclischen Alkaloids Nirurin ( 22 ) eine eindrucksvolle Desaromatisierung von Pyridin beschrieben (Abbildung 1 g) 11. Die Synthese des Azabicyclo[2.2.2]octan(Isochinuclidin)‐Ringsystems von 22 begann mit der alkylierenden Desaromatisierung eines aus dem Pyridin 23 erhaltenen Acylpyridiniumderivats, durch die an C2 eine Allylseitenkette eingeführt wurde 12. Die anschließende Desilylierung lieferte das intermediäre Allenoat 24 , das unter intramolekularer [4+2]‐Cycloaddition in zwei Stufen zu Kernstruktur von Nirurin reagierte.…”