Stereochemistry of reactions at carbon-transition metal .sigma. bonds. .pi.-Cyclopentadienyldicarbonyliron erythro-and threo-3,3-dimethylbutyl-1,2-d2

Abstract

Convenient, stereoselective syntheses of threo-and ¡?r>7/iro-3,3-dimethylbutan-l-oI-/,2-i/2 (1) are described. Reaction of the p-bromobenzenesulfonate esters of 1 with CsHsFeCCOjüMgBr, -Li, or -Na yields ircyclopentadienyldicarbonyliron erythro-and ?Areo-3,3-dimethylbutyl-/,2-d2 (erythro-and threo-2) with >95% inversion of configuration at carbon. Bromination of 2 in pentane, chloroform, carbon disulfide, and dimethylformamide, and iodination in carbon disulfide, all take place with >90% inversion of configuration at carbon. Reaction of 2 with triphenylphosphine, zm-butyl isocyanide, bromine (in methanol), oxygen, cerium(IV) ion, or chlorine (in chloroform) leads to derivatives of 4,4-dimethylpentanoic-2,J-flf2 acid with >90% retention of configuration at carbon. Reaction of 2 with sulfur dioxide in a variety of solvents yields the product of sulfur dioxide insertion, (CH3)3CCHDCHDS02Fe(C0)2Cp, with >95 % inversion of configuration at carbon. Insertion of dimethyl acetylenedicarboxylate into the carbon-iron bond of 2 takes place with >80% retention of configuration at carbon. Thermal decomposition of 2 produces a range of isotopicaUy substituted derivatives of 3,3-dimethyl-l-butene. The mechanistic significance of the results is discussed.The most valuable single type of information to have in characterizing the mechanism of a reaction that makes or breaks bonds at a tetrahedral carbon atom is the stereochemistry of the transformation at that carbon. With this information it is possible to judge whether a reaction involves intermediate free carbon radicals or ions or occurs by Sn2 or Se2 transition states. It is experimentally difficult to obtain stereochemical information about reactions involving transition metal alkyls. Traditional experimental procedures based on the preparation and reaction of enantiomeric organometallic compounds suffer from serious shortcomings. Enantiomerically pure organolithium and magnesium reagents are not generally available,6 and nucleophilic displacements by metallate anions and decarbonylation reactions are complicated by side reactions6 and by thermal instability of the products.12 Further, it is presently difficult to relate the stereochemistry of the starting materials and products in organometallic reactions, since reactions of "known" and reliable stereochemistry have not been established. [13][14][15]

Steric Course of the Rhodium-Catalyzed Decarbonylation of Chiral 4-M ethyl-[1-3H,2-2H1]pentanal

“…mostly, more crowded systems [1][2][3]. It also agrees with the stereochemistry of the reverse proc ess, carbonyl insertion reactions [5][6][7]. This provides further support for the notion [10] that biological carbonyl insertion reactions, even in sterically unhin dered cases like the formation of an acetyl group by "carbonyl insertion" into a metal-methyl bond, also proceed with retention of configuration.…”

Asymmetric transition metal-catalyzed cross-coupling reactions for the construction of tertiary stereocenters

“…First, Fu and co-workers carried out mechanistic experiments of alkyl–alkyl cross-couplings that indicated that the palladium-catalyzed cross-coupling reaction of stereochemically defined alkyl electrophiles proceeds principally with inversion. xxvi Using a strategy pioneered by Whitesides, xxvii Fu and co-workers used the anti -diasteromer of deuterium-labeled primary alkyl tosylate to elucidate the stereochemical outcome of the reaction. As shown in equation 6, alkyl tosylate 40 was subjected to reaction conditions with phenyl-9-borabicyclo[3.3.1]nonane (phenyl-9-BBN) in the presence of catalytic Pd(OAc) 2 to afford 41 in 54% yield and 86% inversion at the carbon bearing the leaving group, corresponding to a syn : anti ratio of 6:1.…”

“…Incorporation of deuterium at the α and β position of primary alkylboranes allows for determination of configuration by analysis of 1 H NMR coupling constants, while introducing little thermodynamic preference for formation of one diastereomer over the other. xxvii The Soderquist and Woerpel groups independently showed that alkylboron reagents undergo palladium-catalyzed cross-coupling reactions with aryl and vinyl halides with retention of configuration (Scheme 22a,b). 73 In a recent report by our laboratory we have demonstrated that the same holds true for nickel-catalyzed cross-coupling reactions with alkyl halides (Scheme 22c).…”

Experimental and Computational Characterization of the Transition State for C–X Bimetallic Oxidative Addition at a Cu–Fe Reaction Center

“…Lastly, no experimentally determined Eyring activation parameters or Hammett reaction constants are available for 72,73 This S N 2 reaction, with [Fp] − as the nucleophile and an alkyl halide as the electrophile, would also be expected to exhibit a large and negative ΔS ⧧ as well as a reaction constant of ρ > 1. The Whitesides stereochemical probe did not react with either (IPr)Cu-Fp or (IMes)Cu-Fp, even after long reaction times or under forcing conditions.…”