A sequential reaction process to assemble polysubstituted indolizidines, quinolizidines and quinolizidine analogues

The ω-iodo-α,β-alkynoates and their ketone, sulfone or phosphonate analogues react with δ-chloropropylamines in MeCN assisted with K₂CO₃ to undergo a sequential S_N2/Michael addition/S_N2/S_N2 reaction process, giving polysubstituted indolizidines or quinolizidines in good to excellent yields. This sequential reaction process is also compatible with three other substituted α,β-alkynoates, affording quinolizidine analogues in moderate to good yields.     

Electroreductive intramolecular coupling of aliphatic cyclic imides with ketones and O-methyloximes

The electroreductive intramolecular coupling of aliphatic cyclic imides with ketones in isopropanol gave five- and six-membered cyclized products. Similarly, the electroreductive intramolecular coupling of aliphatic cyclic imides with O-methyloximes afforded five-, six-, and seven-membered cyclized products. These reactions provide a useful method to synthesize azabicyclo[n.m.0] compounds. The bicyclic products were stereoselectively transformed to the corresponding deoxylated compounds by reduction with NaB(CN)H₃ or Et₃SiH/BF₃·Et₂O.     

Enantioselective approach to indolizidine and quinolizidine scaffolds. Application to the synthesis of peptide mimics

An enantioselective approach to substituted indolizidine and quinolizidine frameworks has been developed. Key steps of the synthesis are the enantioselective, palladium-catalyzed N-allylation of an imide, the nucleophilic allylation of an acyliminium ion and a ring closing metathesis. This general strategy has been applied to the synthesis of indolizidine peptide mimics, starting from a chiral imide derived from l-aspartic acid. It was observed that the preexisting stereogenic center of this substrate has a moderate influence on the stereoselectivity of the electrophilic allylation, which is mainly determined by the sense of chirality of the catalyst.     

Rhodium-catalyzed intramolecular conjugate addition of vinylstannanes to dihydro-4-pyridones: a simple method for stereoselective construction of 1-azabicyclic alkaloids

A straightforward route for the stereoselective synthesis of unsaturated quinolizidines and related higher homologs has been developed. Our results revealed that the rhodium complex [RhCl(cod)]₂ is an effective catalyst for the intramolecular conjugate addition of vinylstannanes to the dihydropyridones leading to the corresponding 1-azabicyclo[m.n.0]alkenes in a moderate to good yield and an excellent diastereoselectivity under neutral conditions at room temperature. This methodology has been successfully applied to the stereoselective synthesis of the racemic lasubine I.     

Synthesis and transformations of sulfur-substituted indolizidines and quinolizidines

3-Sulfolenes 1a-b underwent [4+2] cycloaddition reactions with p-toluenesulfonyl isocyanate to give tetrahydropyridinones 3a-b. Through N-detosylation of 3a-b and subsequent intramolecular cyclization, indolizidine 5a and quinolizidine 5b were synthesized. Useful functional group transformations of compounds 5a-b were also investigated.     

Preparation of some angularly substituted and highly functionalized quinolizidines as building blocks for the synthesis of various alkaloids and related scaffolds of medicinal interest

The epimeric forms of the angularly substituted quinolizidine 6, representing potentially useful building blocks for the synthesis of various alkaloids, have been prepared via a pathway involving two consecutive ring-closing metathesis reactions. Variously hydroxy-protected derivatives (21, 22, and 26-29) of these compounds have also been generated.     

Formal synthesis of (±)-indolizidine 209B

A new method for the synthesis of cis-C-8 methylated indolizidines and quinolizidines has been developed. Straightforward transformations including an isomerization to the trans configuration led to a formal synthesis of (±)-indolizidine 209B.     

Convenient approach to tetrahydro-quinolizin-4-ones by sequential addition of lithium allyldibutylmagnesate to N-allylpyridin-2-ones and ring-closing metathesis reactions

A new strategy based on allylation of N-allylpyridin-2-ones with the lithium allyldibutylmagnesate reagent followed by ring-closing metathesis in a sequential fashion to access the quinolizidine skeleton with olefinic bonds in both rings is reported.     

One-pot tandem route to fused indolizidines and quinolizidines: Application in the synthesis of alkaloids and bioactive compounds

Fused indolizidines and quinolizidines are important skeletons in a variety of natural products and pharmacologically important compounds. A one-pot tandem route from amide to fused indolizidines and quinolizidines is disclosed. This method is conducted in mild conditions and shows well tolerance of functional groups. It is also easy to be scaled up to gram scale and can be applied smoothly to the total synthesis of alkaloids such as (±)-crispine A, (±)-xylopinine, (±)-desbromoarborescidine A, (±)-harmicine and other bioactive substances.     

Synthesis of sulfur-substituted quinolizidines and pyrido[1,2-a]azepines by ring-closing metathesis

Sulfur-substituted quinolizidines and pyrido[1,2-a]azepines (7) can be prepared by ring-closing metathesis (RCM) of 4-(phenylthio)-1,2,5,6-tetrahydropyridin-2-ones (6) bearing terminal alkenyl groups at both N-1 and C-6 positions, which are obtained from 3-(phenylthio)-3-sulfolene (1) in four steps. Some synthetic transformations of 2-(phenylthio)-1,6,9,9a-tetrahydroquinolizin-4-one (7a) and 2-(phenylthio)-1,6,9,10,10a-pentahydropyrido[1,2-a]azepin-4-one (7d) are also reported.