Iminium Catalysis (n → π*)

ChemInform Abstract: Total Synthesis of (+)-Greek Tobacco Lactone.

An enantioselective, protecting-group-free, total synthesis of (+)-Greek tobacco lactone has been achieved by using an organocatalytic Mukaiyama–Michael reaction and a stereospecific oxa-Michael reaction as key steps.

Towards Waltheriones C and D: Synthesis of the Oxabicyclic Core

A route to the oxabicyclic cores of the HIV cytoprotective quinolone alkaloids, waltheriones C and D, is described. The approach relies on a stereospecific transannular bromoetherification followed by reductive debromination. The route can also be rendered enantioselective via enzymatic reduction of a key intermediate (>99:1 er).

Enzymatic Resolution of 3-oxodicyclopentadiene on a Decagram Scale

The chiral building block 3-oxodicyclopentadiene (1) can be readily resolved on a decagram scale by a short sequence consisting of (1) reduction to the corresponding endo-alcohol, (2) enzymatic oxidative resolution with a ketoreductase enzyme to give (+)-1 and the (+)-form of the endo-alcohol, and (3) reoxidation of the (+)-endo-alcohol with another ketoreductase to give (–)-1. With a selectivity factor of 310, the enantiomeric ratios of the resolved (+)-endo-alcohol and (+)-ketone are both >99:1. Both enzymatic oxidations could be performed with a at least 300:1 substrate/catalyst ratio (w/w).

Upper Secondary School and University Level Students’ Perceptions of Extractions in Context: Experiences from a Simple Laboratory Experiment

We discuss the pedagogical challenges associated with the current way of introducing extraction in upper secondary school chemistry education. These challenges were identified based on a survey of upper secondary school textbooks and verified through a questionnaire study. To address the identified challenges, we introduce a simple and effective extraction experiment which focuses on building a deeper conceptual understanding of extraction processes. The operationally simple extraction experiment and the accompanying questionnaire revealed that while students have several chemical misconceptions arising from the use of superficial everyday examples, they have all the necessary knowledge for…

Total Synthesis of (+)-Greek Tobacco Lactone

An enantioselective, protecting-group-free, total synthesis of (+)-Greek tobacco lactone has been achieved by using an organocatalytic Mukaiyama–Michael reaction and a stereospecific oxa-Michael reaction as key steps.

Total Synthesis of Stemoamide, 9a-epi-Stemoamide, and 9a,10-epi-Stemoamide: Divergent Stereochemistry of the Final Methylation Steps

Total syntheses of stemoamide, 9a-epi-stemoamide, and 9a,10-epi-stemoamide by a convergent A + B ring-forming strategy is reported. The synthesis required a diastereoselective late-stage methylation of the ABC stemoamide core that successfully enabled access to three of the four possible diastereomeric structures. For the natural stemoamide series, the diastereoselectivity can be rationalized both by kinetic and thermodynamic arguments, whereas for the natural 9a-epi-stemoamide series, the kinetic selectivity is explained by the prepyramidalization of the relevant enolate.

Conformationally Locked Pyramidality Explains the Diastereoselectivity in the Methylation of trans-Fused Butyrolactones

A stereoselectivity model inspired by the total synthesis of stemona alkaloids is developed to explain why enolate-derived 3,4-fused butyrolactones are methylated with a preference for syn alkylation. The model shows how conformational locking present in nonplanar enolate structures favors syn over anti methylation, due to less significant structural distortions in the syn pathway. The developed model was also successfully used to rationalize selectivities of previously documented methylation reactions. peerReviewed

CCDC 1973338: Experimental Crystal Structure Determination

Related Article: Imre Pápai, Petri M. Pihko, Juha H. Siitonen, Dániel Csókás|2020|Synlett|31|1581|doi:10.1055/s-0040-1707201

CCDC 1827648: Experimental Crystal Structure Determination

Related Article: Katja Kärki, Juha H. Siitonen, Mona Cederström, Sami Kortet, Petri M. Pihko|2018|Synlett|29|1723|doi:10.1055/s-0037-1610109

CCDC 1831369: Experimental Crystal Structure Determination

Related Article: Katja Kärki, Juha H. Siitonen, Mona Cederström, Sami Kortet, Petri M. Pihko|2018|Synlett|29|1723|doi:10.1055/s-0037-1610109

CCDC 997889: Experimental Crystal Structure Determination

Related Article: Juha H. Siitonen, Petri M. Pihko|2014|Synlett|25|1888|doi:10.1055/s-0034-1378273

CCDC 1973339: Experimental Crystal Structure Determination

Related Article: Imre Pápai, Petri M. Pihko, Juha H. Siitonen, Dániel Csókás|2020|Synlett|31|1581|doi:10.1055/s-0040-1707201

CCDC 1827649: Experimental Crystal Structure Determination

Related Article: Katja Kärki, Juha H. Siitonen, Mona Cederström, Sami Kortet, Petri M. Pihko|2018|Synlett|29|1723|doi:10.1055/s-0037-1610109

CCDC 1827647: Experimental Crystal Structure Determination

Related Article: Katja Kärki, Juha H. Siitonen, Mona Cederström, Sami Kortet, Petri M. Pihko|2018|Synlett|29|1723|doi:10.1055/s-0037-1610109