The first example to couple aldehydes and 3-bromo-2-halopropenes in a catalytic asymmetric manner is reported. The coupling reaction is effected by the use of a chiral sulfonamide-Cr complex (prepared in situ from 1d, CrBr3, Fe(III) or from Co(II), Et3N, and Mn), TMSCl, and 2,6-lutidine. The method reported here is operationally simple and scalable, furnishing 3-halohomoallylic alcohols with a synthetically useful level of enantiomeric excess.

Introduced in the late 1980s as a reducing reagent, Tris (2-carboxyethyl) phosphine (TCEP) has now become one of the most widely used protein reductants. To date, only a few studies on its side reactions have been published. We report the observation of a side reaction that cleaves protein backbones under mild conditions by fracturing the cysteine residues, thus generating heterogeneous peptides containing different moieties from the fractured cysteine. The peptide products were analyzed by high performance liquid chromatography and tandem mass spectrometry (LC/MS/MS). Peptides with a primary amine and a carboxylic acid as termini were observed, and others were found to contain amidated or formamidated carboxy termini, or formylated or glyoxylic amino termini. Formamidation of the carboxy terminus and the formation of glyoxylic amino terminus were unexpected reactions since both involve breaking of carbon-carbon bonds in cysteine.

Variable-temperature kinetics studies of the reversible β-methyl elimination reaction of Cp2Hf(CH2CMe3)(μ-Me)B(C6F5)3 (I) to give Cp2Hf(Me)(μ-Me)B(C6F5)3 and CH2CMe2 are reported. Activation enthalpies of 21.3(0.5) and 17.0(0.3) kcal/mol in toluene and chlorobenzene, respectively, are shown to represent the energy barrier for β-methyl migration accompanied by concomitant, solvent-assisted dissociation of [BMe(C6F5)3]- anion from the metal.

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An efficient procedure for SnCl 2 /KI-mediated allylation reactions of formaldehyde with a variety of allylic bromides in aqueous solution is reported. Under conditions developed in this effort, various homoallylic alcohols and 2-halohomoallylic alcohols are produced in good to excellent yields.Formaldehyde is an excellent electrophile for one-carbon elongation of organic substances. However, the intrinsic propensity of formaldehyde monomer to undergo polymerization dramatically limits its synthetic utility. As a result, novel procedures have been developed to suppress polymerization either by using a stable formaldehydeorganoaluminum complex or by generating this substance in situ through the conversion of methanol to formaldehyde or hydrolysis of the Eschenmoser's salt. 1 However, carbon-carbon bond-forming reactions with formaldehyde remain a great challenge.Halohomoallylic alcohols 1a,b, which are comprised of C5 units with isoprene-type skeletons, have been employed as useful building blocks in organic syntheses. 2 In addition, these substances could find additional applications in organic synthesis owing to their possible participation in transition-metal-catalyzed cross-coupling reactions that serve as powerful methods for C-C bond formation. 3 However, the preparation of halohomoallylic alcohols 1a and 1b typically employs multistep routes starting with methyl 3-hydroxy-2-methylpropanoate or other equally complicated pathways (Scheme 1, equations 1 and 2).We envisioned that a straightforward procedure for the synthesis of halohomoallylic alcohols 1 would involve the addition of an appropriate allylic organometallic reagent to formaldehyde (Scheme 2). Although metal-mediated 2-haloallylation of aldehydes can be promoted by using B/ Sn, 4 Sn/HBr, 5 and Fe/Cr, 6 2-haloallylation of formaldehyde has not been reported to date. The conditions employed for B/Sn-and Fe/Cr-mediated 2-haloallylation of aldehydes involve the use of nonaqueous solvents and an inert atmosphere. Thus, the intrinsic polymerization reactivity of monomeric formaldehyde prevents it from being used in Lewis acid catalyzed allylation reactions in organic media. Furthermore, typical thermal cracking of paraformaldehyde to generate formaldehyde monomer is a tedious procedure. Since one could employ commercial aqueous solutions of formaldehyde, metal-mediated Barbier-type allylation reactions of formaldehyde would serve as a facile method to prepare functionalized homoallylic alcohols 1. Scheme 1 Multistep synthesis of 2-halohomoallylic alcohols Scheme 2 Straightforward synthesis of 2-halohomoallylic alcoholsTo the best of our knowledge, only scattered reports describe the metal-mediated allylation reactions of formaldehyde in aqueous media using Sn or Zn, 7 Sn/Al, 8 Sn/ InCl 3 , 9 and In. 10 However, in these processes only simple allylic halides were used. Our investigations aimed at the development of metal-mediated allylation and 2-haloallylation reactions of formaldehyde using water as the solvent. 11 Tin and tin-containing Lewis acids ...