Progress 10/15/01 to 10/14/06
Outputs
Main objective of this program is to develop new, transition metal mediated transformations of agricultural carbohydrates. Expected results of this program will clearly be applicable to the manufacture of useful carbohydrate based products such as detergents, surfactants, and polymers. Ferrier rearrangement is one of the most common reactions using glycal derivatives to obtain their 2,3-unsaturated counterparts using a nucleophile and a protonic or Lewis acid catalyst. Organometallic and carbohydrate chemistry have few overlaps and the project developed here will give rise to a new approach of both organometallic and carbohydrate chemistry through the study of the Ferrier rearrangement using organometallic nucleophiles. Rslts: One of the most powerful organometallic nucleophiles is the Fp anion (Fp = Fe(CO)2Cp). Analysis of initial reaction mixtures did not reveal the formation of an iron complex, but starting material was mainly observed by TLC. First experiment we
attempted suggested that KFp could act as a base and prevent the standard Ferrier rearrangement to proceed normally. Mechanistic studies:Based on initial observations, we decided to further investigate mechanism of the Ferrier rearrangement initiated by BF3*OEt2 in order to determine the best conditions to use for a reaction involving an organometallic nucleophile. It was shown that tri-O-acetyl-D-glucal and BF3*OEt2 lead to an equilibrating mixture of rearranged products which ratios are fairly stable after a certain period of time under the action of an acid catalyst. The exact mechanism of the Ferrier rearrangement is yet to be established. Nevertheless, experimental observations along with spectroscopic studies and the nature of the products obtained are providing enough information to establish the proposed mechanism. Moreover, the formation of the carbocation 2 was never observed to date and only one reference in the literature mentions its formation in a NMR study of the
reaction of hydrofluoric acid with tri-O-acetyl-D-glucal. In our organometallic approach, it seems crucial to be able to form the carbocation 2 in solution and then to let it react with the anionic iron complex (KFp). We decided to explore new approaches for the reaction of organometallic complexes with tri-O-acetyl-D-glucal under Ferrier rearrangement conditions. Further understanding of the Ferrier Rearrangement mechanism:We demonstrated earlier that reaction of KFp with tri-O-acetyl-D-glucal in the presence of BF3*OEt2 did not afford any of the expected organometallic complexes. Several hypotheses were proposed. We designed some experiments that would confirm these hypotheses. Little is known about Ferrier rearrangement involving true anionic species other than Grignard reagents or alkoxides. We therefore decided to investigate another approach involving neutral species and substituting the anionic KFp for its neutral TMSFp 4 analog. We can conclude that TMSFp does not react under
standard Ferrier conditions and do not afford the expected organometallic-glycal species even after 20 h of reaction at room temperature.
Impacts
In order to determine the regioselectivity of the expected addition of the organometallic iron complex to the glycal ring, we are preparing two different glucal derivatives. These two deoxy-glucal derivatives are being prepared according to described procedures. The organometallic Ferrier rearrangement attempts will then be more easily analyzed by GC/MS and we will be able to determine the outcome of the reaction. Conclusion: A number of model experiments have been performed to investigate the reactivity of a nucleophilic organometallic complex (KFp) under standard Ferrier rearrangement conditions. The conclusion arising from these experiments suggest that reaction of KFp and TMSFp with a glycal derivative was unsuccessful. The reasons for the failure of these approaches are not clear yet, but further investigations and different approaches presented in the future work section will provide more data to better understand the behavior of organometallic iron complexes
under Ferrier rearrangement conditions. The fact that NaFp appears to work as a nucleophile (earlier work) suggests that ion pairing effects are of particular importance.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
Agriculture excels at the production of carbohydrates through growing of annual domestic crops and forest products, yet only about 2% of the U.S. chemical feedstock supply comes from agricultural sources. The primary reason for this limited use of carbohydrates as chemical building blocks is not economic, but technological. Few simple, selective, high yield methods for the modification of the native carbohydrate structures exist. The use of transition metal complexes to promote selective structural modification of simple carbohydrates is a method that we believe will bridge this technology gap. The main objective of this program is to develop new, transition metal mediated transformations of agricultural carbohydrates. The expected results of this program will clearly be applicable to the manufacture of useful carbohydrate based products such as detergents, surfactants, and polymers. The Ferrier rearrangement is one of the most common reactions using glycal
derivatives to obtain their 2,3-unsaturated counterparts using a nucleophile and a protonic or Lewis acid catalyst. This reaction was discovered in the late 60s and has been considerably developed in the past decades so that a carbon-Ferrier reaction has been described providing access to C-glycosides (an important class of glycomimetics) and other non-natural carbohydrate derivatives. Organometallic and carbohydrate chemistry have very few overlaps and the project developed here will give rise to a new approach of both organometallic and carbohydrate chemistry through the study of the Ferrier rearrangement using organometallic nucleophiles.
Impacts
A number of model experiments have been performed to investigate the reactivity of a nucleophilic organometallic complex (KFp) under standard Ferrier rearrangement conditions. The conclusion arising from these experiments suggest that reaction of KFp and TMSFp with a glycal derivative was unsuccessful. The reasons for the failure of these approaches are not clear yet, but further investigations and different approaches presented in the future work section will provide more data to better understand the behavior of organometallic iron complexes under Ferrier rearrangement conditions. The fact that NaFp appears to work as a nucleophile (earlier work) suggests that ion pairing effects are of particular importance. This work has been presented as part of seminars held at Iowa State University (February 2005) and Mississippi State University (April 2005).
Publications
- No publications reported this period
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