Rendy Kartika - Cochemist

Brønsted Acid Catalyzed Synthesis of Functionalized 1,4- and 1,6-Dicarbonyl Monosilyl Enol Ethers under Operationally Practical Conditions

Co-reporter:Joshua A. Malone, Joshua P. Van Houten, Moshood O. Ganiu, Binod Nepal, and Rendy Kartika

The Journal of Organic Chemistry October 6, 2017 Volume 82(Issue 19) pp:10659-10659

Publication Date(Web):August 29, 2017

DOI:10.1021/acs.joc.7b01687

Herein, we report an improved protocol for the concise synthesis of functionalized 1,4- and 1,6-dicarbonyl-derived monosilyl enol ethers via ionization of α′-hydroxy silyl enol ethers to generate unsymmetrical silyloxyallyl cations that were subsequently captured by TBS silyl enolates. These transformations were efficiently performed in acetonitrile at room temperature by employing pyridinium triflate as a catalyst. Our new reaction conditions are operationally more practical and broaden the accessibility of various 1,4- and 1,6-dicarbonyl groups, which include diketone, ketoester, and ketothioester functionalities.

Regioselective Functionalization of Enamides at the α-Carbon via Unsymmetrical 2-Amidoallyl Cations

Co-reporter:Mirza A. Saputra, Nitin S. Dange, Alexander H. Cleveland, Joshua A. Malone, Frank R. Fronczek, and Rendy Kartika

Organic Letters May 5, 2017 Volume 19(Issue 9) pp:

Publication Date(Web):April 26, 2017

DOI:10.1021/acs.orglett.7b00962

A new method to functionalize enamides via an intermediacy of unsymmetrical 2-amidoallyl cations is reported. Generated under mild Brønsted acid catalysis, these reactive species were found to undergo addition with various nucleophiles at the less substituted α-carbon to produce highly substituted enamides in high yields with complete control of regioselectivity.

Effects of Solvent and Residual Water on Enhancing the Reactivity of Six-Membered Silyloxyallyl Cations toward Nucleophilic Addition

Co-reporter:Joshua A. Malone, Alexander H. Cleveland, Frank R. Fronczek, and Rendy Kartika

Organic Letters 2016 Volume 18(Issue 17) pp:4408-4411

Publication Date(Web):August 19, 2016

DOI:10.1021/acs.orglett.6b02194

A new strategy for the generation of six-membered unsymmetrical silyloxyallyl cations using catalytic mild Brønsted acid is reported. These reactive intermediates were found to readily undergo direct nucleophilic addition with a broad range of nucleophiles to produce various α,α′-disubstituted silyl enol ether structural motifs. The findings also highlight the significance of the solvent effect and residual water in enhancing the reaction rate.

Functionalization of Silyldienol Ethers at the γ-Position via 2-Silyloxypentadienyl Cations

Co-reporter:Caitlan E. Ayala, Nitin S. Dange, Jacob R. Stepherson, Jeffrey L. Henry, Frank R. Fronczek, and Rendy Kartika

Organic Letters 2016 Volume 18(Issue 5) pp:1084-1087

Publication Date(Web):February 11, 2016

DOI:10.1021/acs.orglett.6b00196

This report describes Brønsted acid catalyzed de novo synthesis of silyldienol ethers bearing tetrasubstituted double bonds via an intermediacy of 2-silyloxypentadienyl cations. The reactivity of these novel cationic intermediates could be modulated and harnessed toward direct nucleophilic additions regioselectively at the γ-position to produce highly functionalized silyldienol ethers with tunable control of the resulting double bond geometry.

Carbazole Annulation via Cascade Nucleophilic Addition–Cyclization Involving 2-(Silyloxy)pentadienyl Cation

Co-reporter:Jacob R. Stepherson, Caitlan E. Ayala, Thomas H. Tugwell, Jeffrey L. Henry, Frank R. Fronczek, and Rendy Kartika

Organic Letters 2016 Volume 18(Issue 12) pp:3002-3005

Publication Date(Web):June 6, 2016

DOI:10.1021/acs.orglett.6b01376

We report a new strategy toward the synthesis of highly functionalized carbazoles via 2-(silyloxy)pentadienyl cation intermediates, which were generated upon ionization of vinyl-substituted α-hydroxy silyl enol ethers under Brønsted acid catalysis. These electrophilic species were found to readily undergo cascade reactions with substituted indoles to generate carbazole molecular scaffolds in good yields via a sequence of regioselective nucleophilic addition, followed by intramolecular dehydrative cyclization.

An expedient synthesis of functionalized 1,4-diketone-derived compounds via silyloxyallyl cation intermediates

Co-reporter:Jacob R. Stepherson, Frank R. Fronczek and Rendy Kartika

Chemical Communications 2016 vol. 52(Issue 11) pp:2300-2303

Publication Date(Web):15 Dec 2015

DOI:10.1039/C5CC09763K

Herein we describe a new method, enabling the synthesis of highly functionalized 1,4-diketones that are readily differentiated as monosilylenol ethers under Brønsted acid catalysis. This synthetically useful chemistry exploited an intermediacy of unsymmetrical silyloxyallyl cations, which were directly captured by silyl enolates to create the targeted α,α carbon–carbon linkages in a regioselective manner. Our reaction conditions proved to be mild, rendering the silylenol ether functionalities intact.

Cooperative benzylic–oxyallylic stabilized cations: regioselective construction of α-quaternary centers in ketone-derived compounds

Co-reporter:Nitin S. Dange, Jacob R. Stepherson, Caitlan E. Ayala, Frank R. Fronczek and Rendy Kartika

Chemical Science 2015 vol. 6(Issue 11) pp:6312-6319

Publication Date(Web):22 Jul 2015

DOI:10.1039/C5SC01914A

We describe a novel reactivity of benzylic–stabilized oxyallyl cations towards regioselective construction of carbon quaternary centers. These synthetically useful intermediates were readily generated upon ionization of aryl substituted α-hydroxy methylenol ethers with catalytic, mild Brønsted acid. The emerging unsymmetrical oxyallyl cations were then directly captured by indoles and other nucleophiles with exquisite control of regioselectivity, predictably at the electrophilic carbon bearing the alkyl substituent to produce highly functionalized, value-added enol ethers.

Triphosgene–pyridine mediated stereoselective chlorination of acyclic aliphatic 1,3-diols

Co-reporter:Andrés Villalpando, Mirza A. Saputra, Thomas H. Tugwell and Rendy Kartika

Chemical Communications 2015 vol. 51(Issue 81) pp:15075-15078

Publication Date(Web):18 Aug 2015

DOI:10.1039/C5CC06365E

We describe a strategy to chlorinate stereocomplementary acyclic aliphatic 1,3-diols using a mixture of triphosgene and pyridine. While 1,3-anti diols readily led to 1,3-anti dichlorides, 1,3-syn diols must be converted to 1,3-syn diol monosilylethers to access the corresponding 1,3-syn dichlorides. These dichlorination protocols were operationally simple, very mild, and readily tolerated by advanced synthetic intermediates.

Mechanistic insights into Brønsted acid-induced nucleophilic substitution of aliphatic imidazole carbamate with halide ions

Co-reporter:Mirza A. Saputra, Rashel L. Forgey, Jeffrey L. Henry, Rendy Kartika

Tetrahedron Letters 2015 Volume 56(Issue 11) pp:1392-1396

Publication Date(Web):11 March 2015

DOI:10.1016/j.tetlet.2015.01.098

Herein we report interesting reactivity of imidazole carbamate towards nucleophilic substitution with halide ions under Brønsted acidic conditions. Depending upon reaction conditions, halide ions could readily attack the carboxyl position and trigger decarboxylative alkyl halide formation. Alternatively, halide ions were also found to competitively undergo nucleophilic acyl substitution, which ultimately results in the generation of carbonate dimerization product.

Brnsted Acid Catalyzed -Functionalization of Silylenol Ethers with Indoles

Co-reporter:Caitlan E. Ayala;Dr. Nitin S. Dange;Dr. Frank R. Fronczek;Dr. Rendy Kartika

Angewandte Chemie International Edition 2015 Volume 54( Issue 15) pp:4641-4645

Publication Date(Web):

DOI:10.1002/anie.201409758

Abstract

A new method which enables carbon–carbon bond formation at the α′-position of silylenol ethers by using catalytic amounts of pyridinium triflate is reported. This chemistry successfully produces, structurally challenging, highly substituted indole-containing silylenol ethers in excellent yields with complete regiocontrol, presumably through silyloxyallyl cation intermediates. Despite the use of Brønsted acid, the silylenol ether moiety does not undergo protodesilylation, thus underscoring the very mild reaction conditions.

Brnsted Acid Catalyzed -Functionalization of Silylenol Ethers with Indoles

Co-reporter:Caitlan E. Ayala;Dr. Nitin S. Dange;Dr. Frank R. Fronczek;Dr. Rendy Kartika

Angewandte Chemie 2015 Volume 127( Issue 15) pp:4724-4728

Publication Date(Web):

DOI:10.1002/ange.201409758

Abstract

A new method which enables carbon–carbon bond formation at the α′-position of silylenol ethers by using catalytic amounts of pyridinium triflate is reported. This chemistry successfully produces, structurally challenging, highly substituted indole-containing silylenol ethers in excellent yields with complete regiocontrol, presumably through silyloxyallyl cation intermediates. Despite the use of Brønsted acid, the silylenol ether moiety does not undergo protodesilylation, thus underscoring the very mild reaction conditions.

Synthesis of Vinyl Chlorides via Triphosgene–Pyridine Activation of Ketones

Co-reporter:Mirza A. Saputra, Ly Ngo, and Rendy Kartika

The Journal of Organic Chemistry 2015 Volume 80(Issue 17) pp:8815-8820

Publication Date(Web):August 6, 2015

DOI:10.1021/acs.joc.5b01137

Herein, we describe a mild method to prepare aliphatic and aromatic vinyl chlorides from their corresponding ketones via triphosgene–pyridine activation in dichloromethane at reflux. The mechanism of this reaction is proposed to involve formation of a putative α-chloro pyridinium carbamate intermediate, which appeared to readily undergo E2 elimination in the presence of pyridine.

Triphosgene–Amine Base Promoted Chlorination of Unactivated Aliphatic Alcohols

Co-reporter:Andrés Villalpando, Caitlan E. Ayala, Christopher B. Watson, and Rendy Kartika

The Journal of Organic Chemistry 2013 Volume 78(Issue 8) pp:3989-3996

Publication Date(Web):March 15, 2013

DOI:10.1021/jo400341n

Unactivated α-branched primary and secondary aliphatic alcohols have been successfully transformed into their corresponding alkyl chlorides in high yields upon treatment with a mixture of triphosgene and pyridine in dichloromethane at reflux. These mild chlorination conditions are high yielding, stereospecific, and well tolerated by numerous sensitive functionalities. Furthermore, no nuisance waste products are generated in the course of the reactions.

Chlorination of Aliphatic Primary Alcohols via Triphosgene–Triethylamine Activation

Co-reporter:Caitlan E. Ayala, Andres Villalpando, Alex L. Nguyen, Gregory T. McCandless, and Rendy Kartika

Organic Letters 2012 Volume 14(Issue 14) pp:3676-3679

Publication Date(Web):July 10, 2012

DOI:10.1021/ol301520d

Activation of primary aliphatic alcohols with triphosgene and triethylamine mixtures afforded either alkyl chloride or diethylcarbamate products, and the switch in selectivity appeared to be driven by sterics. The reaction conditions to achieve this highly useful transformation were unexceptionally mild and readily tolerated by a wide range of sensitive functionalities.

An expedient synthesis of functionalized 1,4-diketone-derived compounds via silyloxyallyl cation intermediates

Co-reporter:Jacob R. Stepherson, Frank R. Fronczek and Rendy Kartika

Chemical Communications 2016 - vol. 52(Issue 11) pp:NaN2303-2303

Publication Date(Web):2015/12/15

DOI:10.1039/C5CC09763K

Herein we describe a new method, enabling the synthesis of highly functionalized 1,4-diketones that are readily differentiated as monosilylenol ethers under Brønsted acid catalysis. This synthetically useful chemistry exploited an intermediacy of unsymmetrical silyloxyallyl cations, which were directly captured by silyl enolates to create the targeted α,α carbon–carbon linkages in a regioselective manner. Our reaction conditions proved to be mild, rendering the silylenol ether functionalities intact.

Cooperative benzylic–oxyallylic stabilized cations: regioselective construction of α-quaternary centers in ketone-derived compounds

Co-reporter:Nitin S. Dange, Jacob R. Stepherson, Caitlan E. Ayala, Frank R. Fronczek and Rendy Kartika

Chemical Science (2010-Present) 2015 - vol. 6(Issue 11) pp:NaN6319-6319

Publication Date(Web):2015/07/22

DOI:10.1039/C5SC01914A

We describe a novel reactivity of benzylic–stabilized oxyallyl cations towards regioselective construction of carbon quaternary centers. These synthetically useful intermediates were readily generated upon ionization of aryl substituted α-hydroxy methylenol ethers with catalytic, mild Brønsted acid. The emerging unsymmetrical oxyallyl cations were then directly captured by indoles and other nucleophiles with exquisite control of regioselectivity, predictably at the electrophilic carbon bearing the alkyl substituent to produce highly functionalized, value-added enol ethers.

Triphosgene–pyridine mediated stereoselective chlorination of acyclic aliphatic 1,3-diols

Co-reporter:Andrés Villalpando, Mirza A. Saputra, Thomas H. Tugwell and Rendy Kartika

Chemical Communications 2015 - vol. 51(Issue 81) pp:NaN15078-15078

Publication Date(Web):2015/08/18

DOI:10.1039/C5CC06365E

We describe a strategy to chlorinate stereocomplementary acyclic aliphatic 1,3-diols using a mixture of triphosgene and pyridine. While 1,3-anti diols readily led to 1,3-anti dichlorides, 1,3-syn diols must be converted to 1,3-syn diol monosilylethers to access the corresponding 1,3-syn dichlorides. These dichlorination protocols were operationally simple, very mild, and readily tolerated by advanced synthetic intermediates.