dixit parmar - Academia.edu (original) (raw)
Papers by dixit parmar
Organic Process Research & Development
Carbonyl reduction is a fundamental transformation that underpins synthetic chemistry. The re-rou... more Carbonyl reduction is a fundamental transformation that underpins synthetic chemistry. The re-routing of carbonyl reduction through less-conventional intermediates allows new selectivity and reactivity to be found in the resulting reaction space. We have shown for the first time that the unusual radical anions formed by electron transfer to the ester carbonyl group can be exploited in additions to alkenes. We have demonstrated that the reductive cyclisations of lactones, triggered by electron-transfer from SmI2-H2O, allow for highly decorated cyclopentane and cycloheptane ring systems to be constructed. Futhermore, the reductive cyclisations of lactones can be exploited in cyclisation cascades. The cascade sequences involve the generation and trapping of unusual radical anions formed from the ester carbonyl followed by the trapping of more conventional radical anions from the carbonyl groups of ketone intermediates.
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Asymmetric Brønsted Acid Catalysis, 2015
Chemical communications (Cambridge, England), Jan 21, 2014
A mild intramolecular fluoro-cyclisation reaction of benzylic alcohols and amines has been develo... more A mild intramolecular fluoro-cyclisation reaction of benzylic alcohols and amines has been developed. This strategy uses commercially available Selectfluor to trigger electrophilic cyclisations to afford fluorinated heterocycles containing 1,3-disubstitution. The dual role of the reagent as a fluorine source and a base is shown to be crucial for reactivity.
Journal of the American Chemical Society, 2012
Unsaturated lactones undergo reductive radical cyclizations upon treatment with SmI(2)-H(2)O to g... more Unsaturated lactones undergo reductive radical cyclizations upon treatment with SmI(2)-H(2)O to give decorated cycloheptanes in a single highly selective operation during which up to three contiguous stereocenters are generated. Furthermore, cascade processes involving lactones bearing two alkenes, an alkene and an alkyne, or an allene and an alkene allow "one-pot" access to biologically significant molecular scaffolds with the construction of up to four contiguous stereocenters. The cyclizations proceed by the trapping of radical anions formed by electron transfer reduction of the lactone carbonyl.
Journal of the American Chemical Society, 2011
A dissertation submitted to the University of Manchester for the degree of Master of Science by R... more A dissertation submitted to the University of Manchester for the degree of Master of Science by Research in the Faculty of Engineering and Physical Sciences 2010 Kieran Richard Price School of Chemistry 2.7. SmI2-H2O cyclisations of di-substituted lactones 2.8. Synthesis of 'Substituted' class 2 cyclisation substrates 2.9. SmI2-H2O cyclisation of 'substituted' class 2 cyclisation substrates 2.10. Product stereochemistry and the mechanism of the cyclisations 2.11. Introduction to cascade cyclisations 2.12. Preparation of cascade cyclisation substrates 2.13 Cascade cyclisations reactions Chapter 3: Conclusion and Future Work 3.1. Areas of Future research Chapter 4: Experimental 4.1. General experimental 4.2. Preparation of Samarium Diiodide 4.3. Experimental Procedures References Declaration No portion of the work referred to in the thesis has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning.
The Journal of Organic Chemistry, 1982
Chemistry - A European Journal, 2010
The use of domino and cascade reactions provides a powerful tool in organic synthetic chemistry. ... more The use of domino and cascade reactions provides a powerful tool in organic synthetic chemistry. The possibility of forming several bonds in one step without isolating the intermediates, changing the reaction conditions, or adding reagents reduces the production costs and simplifies processes. [1] Performing these reactions, for instance, in the presence of chiral organocatalyst complex structures can be obtained with high stereoselectivities. [2] In line with our latest studies towards the development of different asymmetric cascade and domino reactions using organocatalysts, such as chiral Brønsted acids [3] and prolinol derivatives, [4] we became interested in exploring a new enantioselective domino reaction of 1,2-diones with nitroalkenes which would lead to unprecedented polyfunctionalized bicycles. We assumed that the 1,2-diones would undergo a Michael addition to the nitroalkenes, followed by an intramolecular Henry reaction [5] to afford multifunctionalized bicycles containing four stereogenic centers of which two can be neighboring quaternary centers [Eq. (1)]. Initially we proposed a Brønsted base catalyzed activation of the 1,2-dione which would result in the formation of the enolic tautomer of the dione and thus the nucleophilicity of this substrate should be enhanced. Therefore, we started our experimental investigations by reacting cyclohexa-1,2-dione 7 with the b-nitrostyrene (8 a), employing catalytic amounts of the achiral base 1,4-diazabicycloA C H T U N G T R E N N U N G [2.2.2]octane (DABCO). These experiments revealed that base-catalyzed transformations could be achieved and that the bicycloA C H T U N G T R E N N U N G [3.2.1]octan-8one (9 a) can be isolated in good yields. Based on these observations, we decided to develop an asymmetric version of this unprecedented domino reaction. Several chiral organocatalysts were used to study the enantioselective domino Michael-Henry reaction (Figure 1). Based on the successful application of DABCO as an achiral catalyst, we investigated cinchonine 1 as a chiral Brønsted base catalyst [6] and we were able to isolate the product 9 a with moderate enantioselectivities (Table 1, entry 1). In subsequent investigations, we applied cupreidine (2) [7] and trimethylsilyl O-protected cinchonine 3 as catalysts in the domino reaction. Interestingly, we isolated only a racemic mixture of product 9 a (Table 1, entry 2 and 3). These experiments indicated that the asymmetric version of the domino reaction is not controlled by Brønsted base catalysis.
Chemical Communications, 1997
A D 4-manganese(III) porphyrin is utilized to catalyze aziridination of styrene-type substrates w... more A D 4-manganese(III) porphyrin is utilized to catalyze aziridination of styrene-type substrates with enantiomeric excess ranging from 43 to 68%; evidence for a Mn IV reactive intermediate in the catalysis was obtained from spectroscopic studies and organic product analysis.
Organic Process Research & Development
Carbonyl reduction is a fundamental transformation that underpins synthetic chemistry. The re-rou... more Carbonyl reduction is a fundamental transformation that underpins synthetic chemistry. The re-routing of carbonyl reduction through less-conventional intermediates allows new selectivity and reactivity to be found in the resulting reaction space. We have shown for the first time that the unusual radical anions formed by electron transfer to the ester carbonyl group can be exploited in additions to alkenes. We have demonstrated that the reductive cyclisations of lactones, triggered by electron-transfer from SmI2-H2O, allow for highly decorated cyclopentane and cycloheptane ring systems to be constructed. Futhermore, the reductive cyclisations of lactones can be exploited in cyclisation cascades. The cascade sequences involve the generation and trapping of unusual radical anions formed from the ester carbonyl followed by the trapping of more conventional radical anions from the carbonyl groups of ketone intermediates.
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Rueping/Asymmetric Brønsted Acid Catalysis, 2015
Asymmetric Brønsted Acid Catalysis, 2015
Chemical communications (Cambridge, England), Jan 21, 2014
A mild intramolecular fluoro-cyclisation reaction of benzylic alcohols and amines has been develo... more A mild intramolecular fluoro-cyclisation reaction of benzylic alcohols and amines has been developed. This strategy uses commercially available Selectfluor to trigger electrophilic cyclisations to afford fluorinated heterocycles containing 1,3-disubstitution. The dual role of the reagent as a fluorine source and a base is shown to be crucial for reactivity.
Journal of the American Chemical Society, 2012
Unsaturated lactones undergo reductive radical cyclizations upon treatment with SmI(2)-H(2)O to g... more Unsaturated lactones undergo reductive radical cyclizations upon treatment with SmI(2)-H(2)O to give decorated cycloheptanes in a single highly selective operation during which up to three contiguous stereocenters are generated. Furthermore, cascade processes involving lactones bearing two alkenes, an alkene and an alkyne, or an allene and an alkene allow "one-pot" access to biologically significant molecular scaffolds with the construction of up to four contiguous stereocenters. The cyclizations proceed by the trapping of radical anions formed by electron transfer reduction of the lactone carbonyl.
Journal of the American Chemical Society, 2011
A dissertation submitted to the University of Manchester for the degree of Master of Science by R... more A dissertation submitted to the University of Manchester for the degree of Master of Science by Research in the Faculty of Engineering and Physical Sciences 2010 Kieran Richard Price School of Chemistry 2.7. SmI2-H2O cyclisations of di-substituted lactones 2.8. Synthesis of 'Substituted' class 2 cyclisation substrates 2.9. SmI2-H2O cyclisation of 'substituted' class 2 cyclisation substrates 2.10. Product stereochemistry and the mechanism of the cyclisations 2.11. Introduction to cascade cyclisations 2.12. Preparation of cascade cyclisation substrates 2.13 Cascade cyclisations reactions Chapter 3: Conclusion and Future Work 3.1. Areas of Future research Chapter 4: Experimental 4.1. General experimental 4.2. Preparation of Samarium Diiodide 4.3. Experimental Procedures References Declaration No portion of the work referred to in the thesis has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning.
The Journal of Organic Chemistry, 1982
Chemistry - A European Journal, 2010
The use of domino and cascade reactions provides a powerful tool in organic synthetic chemistry. ... more The use of domino and cascade reactions provides a powerful tool in organic synthetic chemistry. The possibility of forming several bonds in one step without isolating the intermediates, changing the reaction conditions, or adding reagents reduces the production costs and simplifies processes. [1] Performing these reactions, for instance, in the presence of chiral organocatalyst complex structures can be obtained with high stereoselectivities. [2] In line with our latest studies towards the development of different asymmetric cascade and domino reactions using organocatalysts, such as chiral Brønsted acids [3] and prolinol derivatives, [4] we became interested in exploring a new enantioselective domino reaction of 1,2-diones with nitroalkenes which would lead to unprecedented polyfunctionalized bicycles. We assumed that the 1,2-diones would undergo a Michael addition to the nitroalkenes, followed by an intramolecular Henry reaction [5] to afford multifunctionalized bicycles containing four stereogenic centers of which two can be neighboring quaternary centers [Eq. (1)]. Initially we proposed a Brønsted base catalyzed activation of the 1,2-dione which would result in the formation of the enolic tautomer of the dione and thus the nucleophilicity of this substrate should be enhanced. Therefore, we started our experimental investigations by reacting cyclohexa-1,2-dione 7 with the b-nitrostyrene (8 a), employing catalytic amounts of the achiral base 1,4-diazabicycloA C H T U N G T R E N N U N G [2.2.2]octane (DABCO). These experiments revealed that base-catalyzed transformations could be achieved and that the bicycloA C H T U N G T R E N N U N G [3.2.1]octan-8one (9 a) can be isolated in good yields. Based on these observations, we decided to develop an asymmetric version of this unprecedented domino reaction. Several chiral organocatalysts were used to study the enantioselective domino Michael-Henry reaction (Figure 1). Based on the successful application of DABCO as an achiral catalyst, we investigated cinchonine 1 as a chiral Brønsted base catalyst [6] and we were able to isolate the product 9 a with moderate enantioselectivities (Table 1, entry 1). In subsequent investigations, we applied cupreidine (2) [7] and trimethylsilyl O-protected cinchonine 3 as catalysts in the domino reaction. Interestingly, we isolated only a racemic mixture of product 9 a (Table 1, entry 2 and 3). These experiments indicated that the asymmetric version of the domino reaction is not controlled by Brønsted base catalysis.
Chemical Communications, 1997
A D 4-manganese(III) porphyrin is utilized to catalyze aziridination of styrene-type substrates w... more A D 4-manganese(III) porphyrin is utilized to catalyze aziridination of styrene-type substrates with enantiomeric excess ranging from 43 to 68%; evidence for a Mn IV reactive intermediate in the catalysis was obtained from spectroscopic studies and organic product analysis.