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]

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Reactions of /A«eo-3,3-dimethylbutyl-./,2-z/2 brosylate (2) and Inflate (4) with nucleophilic metal-containing species have been used to prepare ery/Aro-3,3-dimethylbutyl-/,2-d^phenyl selenide (3), -pyridinecobaloxime (5), and -cyclopentadienyltricarbonylmolybdenum (6); each reaction takes place with inversion of configuration at carbon. Reaction of 3,3-dimethylbutyl-/,2-i/2 bromide (predominantly erythro) (7) with trimethyltin lithium yields trimethyl(3,3-dimethylbutyl-/,2-¿2)tin (8) with ca. 80% inversion of configuration. Treatment of cyclopentadienyldicarbonyliron zAreo-3,3-dimethylbutyl-/,2-í/2 (1) with mercuric chloride leads to rAra>3,3-dimethylbutyl-/,2-j2-mercuric chloride (9).

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Oxygen-17NMR spectra were obtained from the four pairs of isomeric 2-R-2-oxo-1,3,2-dioxaphosphorinanes, where R = OMe (2), NMe, (3), H (4) or Me (5). The isomerism has been previously shown to be confignrational at phosphorus, with one isomer of each pair having an equatorial phosphoryl oxygen (a isomer), and the other an axial orientation for phosphoryl oxygen (b isomer). Only data for the phosphoryl oxygen are reported. Substitution of OMe or NMe, for H or Me produced upfield shifts of 27.941.8ppm. In all cases, the chemical shifts of the a isomers were upfield of the b analogs, with difierences of 7.9, 18.0, 20.3 and 8.6ppm for 2-5, respectively. The absolute values of 1J(31Pi70) were 5-9Hz larger for the a isomers.