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42848-GB1
Borohydrides as Reagent and Catalyst in Carbon-Carbon Bond Formation
Robert E. Sammelson, Ball State University
� From previously published research in my group (Synthesis 2006, 680-686), investigations for the grant continued this past year.� The novel reductive alkylation reaction with sodium borohydride was examined for the synthesis of monosubstituted malononitriles by utilizing aromatic aldehydes as shown in Scheme 1 (carbon-carbon bond formation shown in red).� There were issues with scope and using only aqueous ethanol for the condensation step solved them.� Research is continuing to address these issues and increase the impact of the reaction as shown below.
� 2-Quinolinecarboxaldehyde produces a monosubstituted malononitrile from the carbon-carbon bond forming reductive alkylation, but upon attempted recrystallization or column chromatography a rearrangement occurs.� Nucleophilic attack of the quinoline nitrogen on the carbon of the nitrile followed by a proton transfer and a tautomerization explain how the indolizine is created (Scheme 2).� Single crystal x-ray analysis was applied to confirm the structure of this novel rearranged product.� Under alkylation conditions, only C-alkylation occurs to form a disubstituted malononitrile, which does not undergo rearrangement.
� Based on the selectivity for C-alkylation (verses N-alkylation) on the above quinoline derivative we have explored the reaction of the pyridyl derivatives (Scheme 3).� Additional alkylating agent subsequently allows for N-alkylation.� We are currently now examining the reaction of phenol containing malononitriles.
� When salicylaldehydes (2-hydroxybenzaldehydes) are used the reaction takes a different course where condensation and cyclization precede reduction and new heterocycles are prepared.� This one-pot reaction to produce 4H-chromenes is shown in Scheme 4.� The scope and limitations of this reaction as well as the utilization of the products are still being addressed.
� We have discovered that if we allow the reductive alkylation to return to room temperature and stir for 24 hours that one of the nitriles is converted to an ethyl ester.� This one-pot reaction is shown in Scheme 5.� The scope of this reaction and utilization of the products are still being addressed.
� The resources provided by this ACS-PRF grant have helped my career get off to a swift start. There are several important areas of impact from this funded research.� One is the impact to the chemistry community from the journal publication and numerous oral and poster presentations at local, regional and national meetings.� I was an author of four presentations/posters at the national ACS meeting in Chicago but more importantly I aided three students in presenting posters.� Secondly, there was a great impact on my career.� This grant allowed me to devote my entire efforts this past summer to research and the mentoring of students.� Supplements for Underrepresented Minority Research (SUMR) provided a fellowship for one additional minority student in my research group.� Experiences by all the students (11 undergraduates and 1 graduate) who participated on this project and other projects were again the biggest impact this past year.� They learned a lot of organic chemistry and how to carry out original research and created new knowledge.
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