Sumod A. Pullarkat

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Organization: Nanyang Technological University , Singapore

Department: School of Physical and Mathematical Sciences

Title: (PhD)

TOPICS

Organic Chemistry

Chemicals
References

Palladium catalyzed asymmetric hydrophosphination of α,β- and α,β,γ,δ-unsaturated malonate esters – efficient control of reactivity, stereo- and regio-selectivity

Co-reporter:Xiang-Yuan Yang, Jun Hao Gan, Yongxin Li, Sumod A. Pullarkat and Pak-Hing Leung

Dalton Transactions 2015 vol. 44(Issue 3) pp:1258-1263

Publication Date(Web):12 Nov 2014

DOI:10.1039/C4DT02673J

Both PC-cyclometalated and PCP-pincer type palladium catalysts have recently been found to be robust and efficacious catalysts for the asymmetric P–H addition reaction involving activated olefins. Our studies on the asymmetric P–H addition of diphenylphosphine to malonate ester and α,β,γ,δ-alkylidenemalonate ester revealed for the first time that the catalyst choice can have a dramatic impact in terms of reactivity as well as regio- and stereo-control for this asymmetric hydrofunctionalization reaction. Besides showing significantly contrasting reactivity and stereoselectivity in the hydrophosphination reaction involving malonate ester, in the case of α,β,γ,δ-alkylidenemalonate ester, a novel regiodivergent method was developed with the 1,4-adduct being obtained exclusively with the PC-catalyst while the pincer catalyst produced only the 1,6-adduct.

Asymmetric 1,4-Conjugate Addition of Diarylphosphines to α,β,γ,δ-Unsaturated Ketones Catalyzed by Transition-Metal Pincer Complexes

Co-reporter:Xiang-Yuan Yang, Wee Shan Tay, Yongxin Li, Sumod A. Pullarkat, and Pak-Hing Leung

Organometallics 2015 Volume 34(Issue 20) pp:5196-5201

Publication Date(Web):October 2, 2015

DOI:10.1021/acs.organomet.5b00787

An enantioselective asymmetric 1,4-addition of diarylphosphines to linear α,β,γ,δ-unsaturated dienones was developed. A series of chiral PCP- and PCN-transition-metal (Pd, Pt and Ni) pincers, themselves prepared catalytically via asymmetric hydrophosphination, were sequentially screened to reveal the roles of backbone architecture and metal ion in catalyst design. The selected ester-functionalized PCP-palladium pincer afforded the chiral 1,4-phosphine adducts in excellent yields with up to >99% ee. The same catalyst when utilized for the hydrophosphination of an α,β,γ,δ-unsaturated malonate ester also revealed the critical role played by the ester functionality on the ligand backbone in dictating the enantioselectivity of the 1,6-adduct.

Versatile Syntheses of Optically Pure PCE Pincer Ligands: Facile Modifications of the Pendant Arms and Ligand Backbones

Co-reporter:Xiang-Yuan Yang, Wee Shan Tay, Yongxin Li, Sumod A. Pullarkat, and Pak-Hing Leung

Organometallics 2015 Volume 34(Issue 8) pp:1582-1588

Publication Date(Web):April 16, 2015

DOI:10.1021/acs.organomet.5b00132

A series of chiral C-stereogenic PCP and PCN ligand precursors were prepared in situ from inexpensive achiral starting materials via a simple catalytic asymmetric P–H addition reaction in good overall yields. This facile catalytic method of preparing the ligand backbones renders easy and economical modifications of the electronically crucial para-substituent, chiral functionalities, and donor atoms for different transition metal ions. A one-pot synthetic procedure was used efficiently to prepare the corresponding optically pure pincer complexes. All the new complexes were characterized by NMR and mass spectroscopy. The molecular structures of several selected complexes have also been elucidated by X-ray crystallography. Preliminary studies indicated that minor structural changes on these novel pincer complexes affect their chemical properties significantly when they were applied as catalysts for the reaction between diphenylphosphine and chalcone.

Evaluation of Palladacycles as a Non-Rhodium Based Alternative for the Asymmetric Conjugate 1,4-Addition of Arylboronic Acids to ,-Unsaturated Enones

Co-reporter:Jonathan Wong;Kennard Gan;Houguang Jeremy Chen

Advanced Synthesis & Catalysis 2014 Volume 356( Issue 16) pp:3391-3400

Publication Date(Web):

DOI:10.1002/adsc.201400473

A One-Pot Diastereoselective Self Assembly of C-Stereogenic Copper(I) Diphosphine Clusters

Co-reporter:Xiang-Yuan Yang, Yongxin Li, and Sumod A. Pullarkat

Inorganic Chemistry 2014 Volume 53(Issue 19) pp:10232-10239

Publication Date(Web):September 23, 2014

DOI:10.1021/ic501233w

C-chirogenic diphosphine-based clusters with 8-membered “chairlike” Cu4Cl4L2 and 12-membered “drumlike” Cu6Cl6L3 (L = diphosphine) frameworks were prepared in one-pot syntheses from chiral diphosphines, which were generated in situ via the double hydrophosphination reaction in excellent enantio- and diastereoselectivity. Excellent control over the final molecular architecture of the cluster (drum vs chair) could be achieved by the judicious selection of the source of the copper atoms employed in the synthetic protocol. Each cluster was characterized by single-crystal X-ray crystallography, 1H, 13C, and 31P{1H} NMR spectroscopy. The synthesized clusters were found to exhibit catalytic activity in the hydroboration reaction of α,β-unsaturated enones with excellent yields albeit with low enantioselectivity.

Asymmetric Construction of a Ferrocenyl Phosphapalladacycle from Achiral Enones and a Demonstration of Its Catalytic Potential

Co-reporter:Kennard Gan, Abdul Sadeer, Chang Xu, Yongxin Li, and Sumod A. Pullarkat

Organometallics 2014 Volume 33(Issue 19) pp:5074-5076

Publication Date(Web):September 3, 2014

DOI:10.1021/om5007215

A new approach toward ferrocenyl phosphapalladacycle construction from achiral enones via asymmetric hydrophosphination and subsequent diastereoselective C–H activation is described. Its catalytic efficacy toward C–C bond formation is subsequently illustrated.

N-Heterocyclic Carbene C,S Palladium(II) π-Allyl Complexes: Synthesis, Characterization, and Catalytic Application In Allylic Amination Reactions

Co-reporter:Deepa Krishnan, Meiyi Wu, Minyi Chiang, Yongxin Li, Pak-Hing Leung, and Sumod A. Pullarkat

Organometallics 2013 Volume 32(Issue 8) pp:2389-2397

Publication Date(Web):April 3, 2013

DOI:10.1021/om400110t

A series of five-membered N-heterocyclic carbene C,S palladium(II) π-allyl complexes were successfully developed and characterized. Structural analyses of these complexes revealed that the organopalladium chelates adopt a skew-envelope conformation with a trans disposition of the substituents on the metal chelate rings. Utilizing these C,S palladium(II) π-allyl complexes as catalysts, a catalytic system for the allylic amination reaction has been developed. A series of C–N bond formations between amines and unsymmetrically substituted allylic carbonates could be catalyzed efficiently by complex (±)-9 in a regioselective manner.

Copper(II) Triflate Catalyzed Allylic Arylation of Allylic Alcohols: Direct and Selective Access to C-Allylanilines

Co-reporter:Dr. Ke Chen;Houguang Jeremy Chen;Jonathan Wong;Dr. Jinglei Yang;Dr. Sumod A. Pullarkat

ChemCatChem 2013 Volume 5( Issue 12) pp:3882-3888

Publication Date(Web):

DOI:10.1002/cctc.201300408

Abstract

Copper(II) triflate was used as a simple and commercially available catalyst in the direct amination of allylic alcohols with anilines to provide C-allylanilines. A wide range of functional groups were tolerated under the reaction conditions, and the products were obtained regioselectivity without the need of an activator. A detailed mechanistic investigation was undertaken. The efficacy of this protocol was demonstrated in the conversion of the 2-allylanilines into substituted quinolines through an oxidative cycloaddition reaction.

Synthesis and Characterization of Conformationally Rigid Chiral PyridineN-Heterocyclic Carbene-Based Palladacycles with an Unexpected PdN Bond Cleavage

Co-reporter:Kim Hong Ng;Yongxin Li;Wei Xian Tan;Minyi Chiang

Chirality 2013 Volume 25( Issue 3) pp:149-159

Publication Date(Web):

DOI:10.1002/chir.22116

ABSTRACT

The versatility of a previously developed method for the synthesis of chiral carbene-based palladacycles is demonstrated through the synthesis of two new chiral pyridine-functionalized N-heterocyclic carbene palladacycles with different wingtip groups. The efficiency in their resolution with different counter anions and different chiral amino acid salt auxiliaries has been studied. The absolute stereochemistries of all the chiral compounds were confirmed by single crystal X-ray crystallography. An unexpected Pd–N bond cleavage that resulted in the racemization of the α-carbon center in these complexes has also been investigated. Chirality 25:149–159, 2013. © 2013 Wiley Periodicals, Inc.

Palladacycle-Catalyzed Tandem Allylic Amination/Allylation Protocol for One-Pot Synthesis of 2-Allylanilines from Allylic Alcohols

Co-reporter:Ke Chen;Yongxin Li;Pak-Hing Leung

Advanced Synthesis & Catalysis 2012 Volume 354( Issue 1) pp:83-87

Publication Date(Web):

DOI:10.1002/adsc.201100424

Abstract

An efficient methodology involving the predominant formation of CC bonds is described for the first direct synthesis of 2-allylanilines from allylic alcohols via a one-pot tandem allylic amination/allylation protocol catalyzed by a palladacycle under mild conditions without the requirement for additional activators.

Domino cyclization–alkylation protocol for the synthesis of 2,3-functionalized indoles from o-alkynylanilines and allylic alcohols

Co-reporter:Chang Xu, Vinod K. Murugan and Sumod A. Pullarkat

Organic & Biomolecular Chemistry 2012 vol. 10(Issue 19) pp:3875-3881

Publication Date(Web):15 Mar 2012

DOI:10.1039/C2OB25379H

A practical and efficient protocol for the one-pot synthesis of 2,3-substituted indoles was developed via a palladacycle catalyzed domino cyclization–alkylation reaction involving 2-alkynylanilines and allylic alcohols under mild conditions without any additives.

A tandem Heck–aza-Michael addition protocol for the one-pot synthesis of isoindolines from unprotected amines

Co-reporter:Ke Chen and Sumod A. Pullarkat

Organic & Biomolecular Chemistry 2012 vol. 10(Issue 32) pp:6600-6606

Publication Date(Web):21 Jun 2012

DOI:10.1039/C2OB25854D

A palladacycle-catalyzed tandem Heck-intramolecular aza-Michael reaction protocol has been developed for the one-pot synthesis of 1-substituted isoindolines from N-unprotected 2-bromobenzylamines and acrylates with high yields.

One-pot β-alkylation of secondary alcohols with primary alcohols catalyzed by ruthenacycles

Co-reporter:Xu Chang, Low Wei Chuan, Li Yongxin, Sumod A. Pullarkat

Tetrahedron Letters 2012 Volume 53(Issue 12) pp:1450-1455

Publication Date(Web):21 March 2012

DOI:10.1016/j.tetlet.2012.01.025

A ruthenacycle-catalyzed one-pot β-alkylation of secondary alcohols with primary alcohols is described. A survey of four C–N chelate ruthenacycles synthesized via the cyclometallation reaction of phenylmethanamine, N-methylphenylmethanamine, N,N-dimethylphenylmethanamine, and naphthalen-1-ylmethanamine with [(η6-C6H6)RuCl2]2 was undertaken. All four complexes were found to be active with the phenylmethanamine-based ruthenacycle showing the best combination of reactivity and product selectivity among the four. An expanded scope of substrates was also studied with the inclusion of unsaturated primary alcohols. The reactivity trend observed gave insights into the role of hydrogen bonding in the catalytic mechanism involving transfer hydrogenation between the substrates and the transition metal catalyst.A ruthenacycle-catalyzed one-pot β-alkylation of secondary alcohols with primary alcohols is described. A survey of four C–N chelate ruthenacycles synthesized via the cyclometallation reaction of phenylmethanamine, N-methyl-1-phenylmethanamine, N,N-dimethyl-1-phenylmethanamine, and naphthalen-1-ylmethanamine with [(η6-C6H6)RuCl2]2 was undertaken.

New thioether–dithiolate complexes of Cp∗Ir and some reactivity features

Co-reporter:Chang Xu, Yongxin Li, Lai Yoong Goh, Sumod A. Pullarkat

Journal of Organometallic Chemistry 2012 696(26) pp: 4207-4214

Publication Date(Web):

DOI:10.1016/j.jorganchem.2011.09.012

Chiral Phosphapalladacycles as Efficient Catalysts for the Asymmetric Hydrophosphination of Substituted Methylidenemalonate Esters: Direct Access to Functionalized Tertiary Chiral Phosphines

Co-reporter:Chang Xu, Gan Jun Hao Kennard, Felix Hennersdorf, Yongxin Li, Sumod A. Pullarkat, and Pak-Hing Leung

Organometallics 2012 Volume 31(Issue 8) pp:3022-3026

Publication Date(Web):March 20, 2012

DOI:10.1021/om201115n

A chiral palladacycle-promoted enantioselective asymmetric hydrophosphination of substituted methylidenemalonate esters using diphenylphosphine that provides direct access to chiral tertiary phosphines is reported. Screening of three easily accessible C,N and C,P palladacycles as catalysts for this synthetic scenario provided insights into critical factors in catalyst design that influence the activation and stereochemistry in Pd(II)-catalyzed asymmetric P–H addition reactions involving such activated substrates.

Direct Synthesis of Chiral Tertiary Diphosphines via Pd(II)-Catalyzed Asymmetric Hydrophosphination of Dienones

Co-reporter:Yinhua Huang, Renta Jonathan Chew, Yongxin Li, Sumod A. Pullarkat, and Pak-Hing Leung

Organic Letters 2011 Volume 13(Issue 21) pp:5862-5865

Publication Date(Web):October 10, 2011

DOI:10.1021/ol202480r

A highly diastereo- and enantioselective Pd(II)-catalyzed hydrophosphination of dienones with Ph2PH involving formation of double C*–P bonds has been developed, providing a series of chiral tertiary diphosphines (chiral PCP pincer ligands) in high yields. A catalytic cycle for the reaction was proposed.

Efficient Iridium-Thioether-Dithiolate Catalyst for β-Alkylation of Alcohols and Selective Imine Formation via N-Alkylation Reactions

Co-reporter:Chang Xu, Lai Yoong Goh, and Sumod A. Pullarkat

Organometallics 2011 Volume 30(Issue 23) pp:6499-6502

Publication Date(Web):November 15, 2011

DOI:10.1021/om200883e

An Ir-thioether-dithiolate complex, [Cp*Ir(η3-tpdt)] (Cp* = η5-C5Me5, tpdt = S(CH2CH2S–)2), is evaluated for its catalytic potential in the β-alkylation of secondary alcohols and the N-alkylation of amines with alcohols. The β-alkylation reaction proceeded efficiently under low catalyst loading and in the absence of any sacrificial hydrogen additive with only water being formed as the coproduct. The same complex also proved to be efficient in the synthesis of imines via the N-alkylation reaction. The predominant formation of imines, rather than amines, in this reaction is a deviation from the product selectivity usually observed in similar N-alkylation reactions involving organometallic catalysts.

Domino cyclization–alkylation protocol for the synthesis of 2,3-functionalized indoles from o-alkynylanilines and allylic alcohols

Co-reporter:Chang Xu, Vinod K. Murugan and Sumod A. Pullarkat

Organic & Biomolecular Chemistry 2012 - vol. 10(Issue 19) pp:NaN3881-3881

Publication Date(Web):2012/03/15

DOI:10.1039/C2OB25379H

Palladium catalyzed asymmetric hydrophosphination of α,β- and α,β,γ,δ-unsaturated malonate esters – efficient control of reactivity, stereo- and regio-selectivity

Co-reporter:Xiang-Yuan Yang, Jun Hao Gan, Yongxin Li, Sumod A. Pullarkat and Pak-Hing Leung

Dalton Transactions 2015 - vol. 44(Issue 3) pp:NaN1263-1263

Publication Date(Web):2014/11/12

DOI:10.1039/C4DT02673J

A tandem Heck–aza-Michael addition protocol for the one-pot synthesis of isoindolines from unprotected amines

Co-reporter:Ke Chen and Sumod A. Pullarkat