Methyl tetramates

Cadmium tert.-Butylthio-methyl-(tetramer) XIII/2a, 908 f. 

Scheme 37 2012OL3862). Treatment of the bromoacetamide 173 with samarium iodide and HMPA followed by diazomethane gives the methyl tetramate 174. The latter intermediate allowed completion of a formal synthesis of palau imide (34). Pettus and coworkers later used this methodolgy in an approach to tetrapetalone (24) (2014OL1294). 

Methoxy-3-pynolin-2-ones (methyl tetramates) have been prepared by the cyclocondensation of y-halo-p-alkoxybutenoates 310 (e.g., = OMe)... 

Due to the prevalence of the 4-methoxy-3-pyrrohn-2-one moiety (methyl tetramates) in natural products (see Figure 4), a variety of methods have been developed to convert tetramic acids into methyl tetramates. In the context of the total synthesis of althiomycin (28), Inami and Shiba used diazomethane to convert 4 into methyl tetramate (485), which was accompanied by the formation of 2-methoxy isomer 486 (Scheme 133 1984TL2009, 1985BCSJ352). Others have used diazomethane to prepare... 

The ratio of cycHc to linear oligomers, as well as the chain length of the linear sdoxanes, is controlled by the conditions of hydrolysis, such as the ratio of chlorosilane to water, temperature, contact time, and solvents (60,61). Commercially, hydrolysis of dim ethyl dichi oro sil a n e is performed by either batch or a continuous process (62). In the typical industrial operation, the dimethyl dichi orosilane is mixed with 22% a2eotropic aqueous hydrochloric acid in a continuous reactor. The mixture of hydrolysate and 32% concentrated acid is separated in a decanter. After separation, the anhydrous hydrogen chloride is converted to methyl chloride, which is then reused in the direct process. The hydrolysate is washed for removal of residual acid, neutralized, dried, and filtered (63). The typical yield of cycHc oligomers is between 35 and 50%. The mixture of cycHc oligomers consists mainly of tetramer and pentamer. Only a small amount of cycHc trimer is formed. 

Several ester enolates have also been examined by X-ray crystallography. The enolates of /-butyl propionate and /-butyl 3-methylpropionate were obtained as TMEDA solvates of enolate dimers. The enolate of methyl 3,3-dimethylbutanoate was obtained as a THF-solvated tetramer. 

Fig. 7.3. Crystal structures of some lithium etiolates of ketones. (A) Unsolvated hexameric enolate of methyl t-butyl ketone (B) tetrahydrofuran solvate of tetramer of enolate of methyl r-butyl ketone (C) tetrahydrofuran solvate of tetramer of enolate of cyclopentanone (D) dimeric enolate of 3,3-dimethyl-4-(r-butyldimethylsiloxy)-2-pentanone. (Structural diagrams are reproduced from Refs. 66-69.) by permission of the American Chemical Society and Verlag Helvetica Chimica Acta AG.

Figure 4.17 Crystal and molecular structure of (LiMe)4 showing (a) the unit cell of lithium methyl, (b) the LijCj skeleton of the tetramer viewed approximately along one of the threefold axes, (c) the 7-coordinate environment of each C atom, and (d) the (4 -I- 3 -I- 3)-coordinate environment of each Li atom. After ref. 93, modified to include Li—H contacts.

The core unit of the chromatin, the nucleosome, consists of histones arranged as an octamer consisting of a (H3/ H4)2-tetramer complexed with two histone H2A/H2B dimers. Accessibility to DNA-binding proteins (for replication, repair, or transcription) is achieved by posttranslational modifications of the amino-termini of the histones, the histone tails phosphorylation, acetylation, methylation, ubiquitination, and sumoyla-tion. Especially acetylation of histone tails has been linked to transcriptional activation, leading to weakened interaction of the core complexes with DNA and subsequently to decondensation of chromatin. In contrast, deacetylation leads to transcriptional repression. As mentioned above, transcriptional coactivators either possess HAT activity or recruit HATs. HDACs in turn act as corepressors. 

This has been found to be a general reaction for many types of olefins. It has also been applied to highly branched structures, such as 2,4,4-trimethyl-2-pen-tane and propylene trimers and tetramers [177], to unbranched olefins with internal double bonds, such as methyl oleate [178] and tricosane, and to a-ole-fins [179], In all cases the data indicate that the reaction occurs at the double... 

Fig. 7. Calculated time/conversion curves and experimental data points in the anionic polymerization of MMA (C0 = 0.1 mol/1) initiated by methyl-a-lithioisobutyate (C0 = 0.05 mol/1) at 25 °C in THF (Products higher than the tetramer are omitted) (A. H. E. Muller, L. Lochmann, J. Trekoval, Ref.S0))...

Integration of the H-NMR spectrum shows 55% of tetramer proportions of individual isomers were estimated from GC/MS data. Tetramer mixtures show an asymmetrical, vinyl resonance centered at S 5.40, and asymmetrical, methyl resonances centered at 8 1.70 ( vs. Me4Si in CS2 solution). Integration of the H-NMR spectrum. 

Tetramethyl-l,2-cyclohexanedione (310) and methyl 2,3-diaminopropio-nate (311) (liberated in situ) gave methyl 5,5,8,8 - tetrame th y 1 - 5,6,7,8, -tetra-hydro-2-quinoxalinecarboxylate (312) [MeOH, molecular sieve (3A), reflux, 5 h 45% note the spontaneous aerial ( ) oxidation].737... 

Transformations through 1,2-addition to a formal PN double bond within the delocalized rc-electron system have been reported for the benzo-l,3,2-diazaphospholes 5 which are readily produced by thermally induced depolymerization of tetramers 6 [13] (Scheme 2). The monomers react further with mono- or difunctional acyl chlorides to give 2-chloro-l,3,2-diazaphospholenes with exocyclic amide functionalities at one nitrogen atom [34], Similar reactions of 6 with methyl triflate were found to proceed even at room temperature to give l-methyl-3-alkyl-benzo-l,3,2-diazaphospholenium triflates [35, 36], The reported butyl halide elimination from NHP precursor 13 to generate 1,3,2-diazaphosphole 14 upon heating to 250°C and the subsequent amine addition to furnish 15 (Scheme 5) illustrates another example of the reversibility of addition-elimination reactions [37],... 

The size of the ligand is crucial in deciding the degree of association, as shown by the very similar structural features of methyl- and "butyllithium derivatives. With hexameric structures in cyclohexane, the addition of diethyl ether affords tetramers in both cases. Further demonstrating the importance of the donor, the two-dimensional phenyl ligand also adopts a tetrameric structure in diethyl ether [Li(OEt2)Ph]4, which upon addition of the bidentate... 

The precipitated silica (J. Crosfield Sons) was heated in vacuo at 120° for 24h. before use. Two grades of surface areas 186 and 227 m g l (BET,N2), were used during this project. Random copolymers, poly(methyl methacrylates) and polystyrene PS I were prepared by radical polymerization block polymers and the other polystyrenes were made by anionic polymerization with either sodium naphthalene or sodium a methylstyrene tetramer as initiator. The polymer compositions and molecular weights are given in Table I. 

A polymeric structure is exhibited by "beryllium dimethyl," which is actually [Be(CH3)2] (see the structure of (BeCl2) shown earlier), and LiCH3 exists as a tetramer, (LiCH3)4. The structure of the tet-ramer involves a tetrahedron of Li atoms with a methyl group residing above each face of the tetrahedron. An orbital on the CH3 group forms multicentered bonds to four Li atoms. There are numerous compounds for which the electron-deficient nature of the molecules leads to aggregation. 

---