This paper reviews all recent attempts to prepare tetra-tert-butylethylene. Some of the synthetic pathways approached this molecule very close but failed during the last step. According to recent DFT calculations this alkene should be a stable molecule with a strain energy in the range of 93 kcal/mol. Since all synthetic approaches failed new methodologies have to be developed, that is either synthesis of the perfluoro derivative of this alkene or the reaction of the radical cation or the radical anion of di-tert-butylmethane with the carbene by a crossed beam technique in the gas phase.(2) Di-tert-butyldiisopropylpropylethylene (3) Tri-tert-butylethylethylene (4) Tetraaldehyde (5) Di-tert-butylcarbene (6) anti-fenchylidenefenchane (7) 1,2-Di-tert-butyl-3,3,5,5-tetramethylcyclopentene (8) Tetra-tert-butylethane (9) 1,1-Dimethyl-2-tert-butylcyclopropane

A novelly developed tweezing-adsorptive bubble separation (ABS) method for the enrichment of metalloenzymes (laccase C and horseradish peroxidase) is introduced. The method is based on the chelation of the enzymes' active center and can also be applied for analysis. N-(2-acetamido)iminodiacetic acid served as a chelator and was synthesized with an octyl unit to become ADA-C8. Laccase was enriched 13.3-fold (66.31% recovery) and HPOX 17.8-fold (85.34%) without a significant loss of enzymatic activity. To prove that the entire enzyme is tweezed at the active center, ABS trials were done using ADA-C8 already complexed with Cu2+ and Fe3+. As only marginal enrichment occurred (ER laccase, 0.17; ER HPOX, 0.44), no chelating effect was concluded. It was determined how the chelation toward the active center was directed by applying other chelators such as EDTA, NTA, N,N-dimethylaminoglycine, oxalic acid, malonic acid, adipinic acid, and tripropylamine, which are similar in structure to ADA-C8. The results concluded that the chelation is 3-fold coordinated on the type 1 copper center of laccase, whereas that of HPOX only 1-fold at Fe3+ and additionally at the cationic amino acid arginine, which is also located at the active center. Tweezing-ABS has been proven to selectively and effectively enrich metalloenzymes.

Sterically congested adamantylideneadamantanes (1b-g) (X = Br, Cl, F, OH, OEt, OCOCH(3)), homoallylically substituted with equatorial groups (X), react with bromine in 1,2-dichloroethane to give a stable bromonium ion intermediate or a substitution product depending on the nature of the substituent and on the bromine concentration. The nature of the substituent markedly affects the formation constant of the 1:1 pi-complexes, as well as of the formation constant and reactivity of bromonium ion intermediates. The different reactivity of the ionic intermediates, which depends on the nature of substituents, is attributed to bromonium or bromocarbenium character of the intermediate, with the support of theoretical investigations. Ab initio calculations on 1:1 adamatylideneadamantane-Br(2) complexes (2a-f) show that the substituent affects the stability of these species through electrostatic and dispersion effects. Solvent effects may also contribute to modulate the relative stability of these species.

A straightforward procedure for the synthesis of 4-methyl-1,3-dioxolane-4-carbaldehydes 2 is reported. The new procedure involves m-CPBA oxidation of 5-methyl-4H-1,3-dioxins 5 in dichloromethane to give 4-(m-chlorobenzoyloxy)-5-hydroxy-5-methyl-1,3-dioxanes 6 and acid-catalyzed rearrangement of 6 to carbaldehydes 2. By using commercially available m-CPBA the oxidation and rearrangement can be carried out as a one-pot reaction. The procedure is also applicable to 4H-1,3-dioxins. Oxidation of 5 in methanol led to 4-methoxy-5-hydroxy-1,3-dioxanes 7, which did not undergo acid-catalyzed rearrangement.Derivatives of 2-C-methylglyceraldehyde 1 such as 4-methyl-1,3-dioxolane-4-carbaldehydes 2 and related 4-hydroxymethyl-4-methyl-1,3-dioxolanes 3 ( Figure 1) have found many applications in natural product syntheses, e.g., the synthesis of brevetoxin B, 1 bicyclomycin, 2 tocopherol, 3 and pheromones. 4 Several methods have been developed for the preparation of 2 and 3. Enantiomerically pure carbaldehydes 2 and corresponding open-chain derivatives have been obtained from D-mannitol, 1,5 D-glucose, 6 penam derivatives, 7 or by resolution of racemic 3 8 in multi-step reaction sequences. Other syntheses involve enzymatic methods to give hydroxymethyl derivatives 3, which have been oxidized to carbaldehydes 2. 9 Sharpless epoxidation of 2-methyl-2-propen-1-ol and monoprotected 2-methylene-1,3-propanediol, respectively, or Sharpless dihydroxylation of O-protected 2-methyl-2-propen-1-ol derivatives gave precursors for the synthesis of 2 with 47-95% ee. 8,10 Figure 1Recently we reported a novel nickel-catalyzed asymmetric double-bond isomerization of 5-methylene-1,3-dioxanes 4, which afforded optically active 5-methyl-4H-1,3-dioxins 5 with high ee (5d 92% ee). 11 We envisaged, that dioxins 5 might be suitable building blocks for the synthesis of 1 by m-CPBA oxidation and subsequent hydrolysis (Scheme 1). To our knowledge the m-CPBA oxidation of cyclic vinyl acetals has not yet been investigated, but we concluded from the well-known m-CPBA oxidation of cyclic vinyl ethers 12 that reaction of 5 with m-CPBA should lead to acylals 6 rather than to epoxides, which should be hydrolyzed to give 1. Scheme 1However, first experiments on the m-CPBA oxidation of 5d in dichloromethane surprisingly afforded 4-methyl-1,3-dioxolane-4-carbaldehyde 2d in a single step upon distillative workup of the crude reaction mixture (Scheme 1). 11 Since 2d still carries the tert-butyl substituent in the 2-position of the dioxolane ring, we argued that the primarily formed oxidation product immediately undergoes either a thermal or an acid-catalyzed rearrangement. In order to get further information about the mechanism of this unexpected type of rearrangement, we studied the m-CPBA oxidation of 5-methyl-4H-1,3-dioxins 5a-e in various solvents (Tables 1, 2). Treatment of 5-methyl-4H-1,3-dioxins 5a-e with commercially available m-CPBA 13 in methanol readily afforded a diastereomeric mixture of 4-methoxy-5-hydroxy-1,3-dioxanes 7a-e (Scheme 2, Table 1). Acetals ...