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palladium-catalyzed cross-coupling catalysis silanol Denmark, Scott E. Denmark, Scott E. Moore, Jeffrey S. Burke, Martin D. Girolami, Gregory S. Werner, Nathan S. 2011-08-26T15:20:42Z 2013-08-27T10:00:18Z 2011-08-26T15:20:42Z 2011-08 The palladium-catalyzed cross-coupling of allylic silanolate salts with a wide variety of aromatic bromides was developed. The coupling of sodium allyldimethylsilanolate and 2-butenyldimethylsilanolate required extensive optimization to deliver the expected products in high yields. The reaction of the allyldimethylsilanolate takes place at 85 °C under “ligand-less’ conditions in 1,2-dimethoxyethane with allylpalladium chloride dimer (2.5 mol %) to afford 73–95% yields of the allylation products. Both electron-rich and sterically hindered bromides reacted smoothly, whereas electron-poor bromides cross-coupled in poor yield because of a secondary isomerization to the 1-propeneyl isomer (or concommitant polymerization). A modified protocol that employs an electron-rich phosphine ligand (SPhos), a lower reaction temperature (40 °C), and a less polar solvent (toluene) delivers the expected products from electron-poor bromides without isomerization. The 2-butenyldimethylsilanolate (E/Z, 80:20) required additional optimization to maximize the formation of the branched (gamma-coupled) product and resulted in the development of two distinct protocols for gamma-selective coupling. The first protocol took advantage of a remarkable influence of added alkenes (dibenzylideneacetone and norbornadiene) and led to good selectivities for a large number of electron-rich and electron-poor bromides in 40–83% yields. However, bromides containing coordinating groups (particularly in the 2-position) gave lower, and in one case even reversed, site-selectivity. Electron-rich aromatic bromides reacted sluggishly under this protocol and led to lower product yields. The second protocol employed a sterically bulky phosphonium tetrafluoroborate salt (t-BuCy2PH+BF4−) and resulted in 73–94% yields and excellent site-selectivity (gamma/alpha, 25:1–>99:1) in the coupling of electron-rich, electron-poor, sterically hindered, and heteroaromatic bromides. The use of a configurationally homogeneous (Z)-silanolate and nontransferable diethyl groups were critical to achieving excellent results. A unified mechanistic picture involving initial gamma-transmetalation followed by direct reductive elimination or sigma–pi isomerization can rationalize all of the observed trends. The stereochemical course of palladium-catalyzed cross-coupling reactions of an enantioenriched, alpha-substituted, allylic silanolate salt with aromatic bromides was determined. The allylic silanolate salt was prepared in high geometrical (Z/E, 94:6) and high enantiomeric (94:6 er) purity by a copper-catalyzed SN2’ reaction of a resolved carbamate. Eight different aromatic bromides underwent cross-coupling with excellent constitutional site-selectivity and excellent stereospecificity. Stereochemical correlation established that the transmetalation event proceeds through a syn SE’ mechanism with is interpreted in terms of an intramolecular delivery of the arylpalladium electrophile through a key intermediate that contains a discrete Si–O–Pd linkage. The catalytic, asymmetric palladium-catalyzed cross-coupling of sodium 2-butenylsilanolate with aromatic bromides was investigated. A wide range of chiral ligands including olefin, bidentate phosphine, monodentate phosphine, and cyclic and acyclic stereogenic at phosphorus ligands were evaluated. Commonly used chiral, bidentate phosphine ligands provided ineffective palladium-catalysts for the coupling of 2-butenyldimethylsilanolate with aromatic bromides. A catalyst derived from the monodentate phosphine ligand neomenthyldiphenylphosphine (20 mol %) and Pd(dba)2 (5 mol %) provided moderate enantioselectivity (75:25 er) and modest site-selectivity (5.7:1 gamma/alpha) in the coupling. Increased site-selectivity (up to >99:1) was obtained from reactions employing bulky di or trialkylphosphine ligands. Item withdrawn by Alexis Thompson (athmpsn1@illinois.edu) on 2011-07-11T19:36:46Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 2 Werner_Nathan.docx: 4840619 bytes, checksum: 73cc057b0da5723f0ac3c9db1a7ea444 (MD5) Werner_Nathan.pdf: 2703275 bytes, checksum: 9dba12df809a3e246b2ec13fa921e7b3 (MD5) Made available in DSpace on 2011-08-26T15:20:42Z (GMT). No. of bitstreams: 3 Werner_Nathan.pdf: 2699822 bytes, checksum: bed436992ed07436f1732a676387ca84 (MD5) license.txt: 4063 bytes, checksum: d8aa8c35fc54e851a11d734bd9851eaa (MD5) Werner_Nathan.docx: 4840603 bytes, checksum: f6f008ef10d13dab8a45ee3a17a0d724 (MD5) Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by William Ingram (wingram2@illinois.edu) on 2011-08-26T15:25:30Z Item is restricted until 2013-08-26T15:25:28Z Item reinstated by Sarah Shreeves (sshreeve@illinois.edu) on 2013-08-27T10:00:17Z Item was in collections: University of Illinois Dissertations and Theses (ID: 204) Dissertations and Theses - Chemistry (ID: 676) No. of bitstreams: 4 Werner_Nathan.pdf.txt: 415720 bytes, checksum: 6c7103b35fb51a476a9fd2cbed576643 (MD5) Werner_Nathan.pdf: 2699822 bytes, checksum: bed436992ed07436f1732a676387ca84 (MD5) license.txt: 4063 bytes, checksum: d8aa8c35fc54e851a11d734bd9851eaa (MD5) Werner_Nathan.docx: 4840603 bytes, checksum: f6f008ef10d13dab8a45ee3a17a0d724 (MD5) Item released from any restrictions by Sarah Shreeves (sshreeve@illinois.edu) on 2013-08-27T10:00:18Z http://hdl.handle.net/2142/26271 en Copyright 2011 Nathan S. Werner silanolate aromatic bromide allyl arene allylic site-selective asymmetric enantioselective stereospecific diastereoselective syn SE' stereochemical course The development of palladium-catalyzed cross-coupling reactions of allylic silanolate salts with aromatic bromides Chemistry 1413 Chemistry 0335 University of Illinois at Urbana-Champaign Dissertation Ph.D. PHD:Chemistry -UIUC 10KS0335PHD