Methylene , structure

Benzothiazoline, N-methyl-2-methylene-structure, 6, 238 Benzothiazolines aromatization, 6, 270 oxidation, 6, 272 structure, 6, 238 synthesis, 6, 323, 325 Benzothiazoline-2-thione, 3-methyl-in organic synthesis, 6, 329 Benzothiazoline-2(3 f/)-thiones tautomerism, 6, 248 Benzothiazolin-2-one alkylation, 6, 286 Benzothiazolin-2-one, 3-methyl-hydrazone... 

The phosphine-catalysed reaction between an aldehyde and an acrylate yielding p-hydroxy-ot-methylene structures was first described by Morita et al. in 1968 (Scheme 37) [85]. In 1972, Baylis and Hillman [86] used a tertiary amine as catalyst and improved the yield of this reaction. 

The aldehyde can be replaced by an imine and the reaction is then called the aza-Baylis-Hillman reaction [87, 88]. (3-Amino-a-methylene structures obtained in this way could further be converted to a range of biologically important molecules, such as p-amino acids [89]. First reaction of this kind was published in 1984 [90]. Tosylimines and ethylacrylate reacted in the presence of DABCO as catalyst to give p-aminoesters. First three-component aza-Baylis-Hillman reaction was published in 1989 by Bertenshaw and Kahn [91], with imine formation in situ from an aldehyde and an amine. In the presence of triphenylphosphine as catalyst, the reaction with methylacrylate led to the formation of the p-amino-ot-methylene esters and ketones in good yields (Scheme 38). 

The scope was then extrapolated to the two-step three-component aza-Baylis-Hillman setup to obtain (3-amino-a-methylene structures. A two-step approach was chosen to avoid the competition between the aldehyde and the imine for the reaction with the enolate, that would lead to mixtures of Baylis-Hillman and aza-Baylis-Hillman adducts, that is (3-hydroxy and (3-amino esters [87]. 

The methylene structure has been established by x-ray analysis, but the methyl derivative has not been so defined, although NMR spectroscopic data have shown that the methyl group unsymmetrically bridges two osmium atoms with a three-center, two-electron... 

The < vo-methylene structure of the 6-methylenedibenzo[<7,g][l,3,6]trithiocine 11 was determined by X-ray crystallographic analysis. Any axis, plane, or point of symmetry does not exist in the molecule in the crystalline state, although the two benzene rings and two < vo-methylene hydrogen atoms are equivalent in solution as is evident from the H NMR spectrum <1999T10057>. 

The classical silica gel chromatographic method for determination of percent olefins in shale oils was studied and found wanting, mainly because of cross-contamination from high levels of olefins and heteroatom-containing compounds. This paper describes a new hydroboration/oxidation procedure for olefins, and reports its use in hydrocarbon-type analysis of both whole shale oils and distillate fractions. Percent composition values for three whole oils ranged as follows saturates, 13-26 olefins, 16-20 aromatics, 5-14 polar compounds, 41S2. A discussion of IR analysis for relative amounts of specific olefin types such as terminal, internal trans, and methylene structures is included. 

The 725 cm" rocking mode doublet is presented in Figure 3. The peaks at 731 and 720 cm for this sample are approximately 15 times the intensity of the amorphous wagging modes. The 720 cm limiting frequency is assigned to long trans sequences in the amorphous and crystalline phases. For these samples, most of the methylene structures are in the crystal, and the band is associated with this phase predomi-... 

Fig. 11.12 Equilibrium between methyl and /i-hydrido-/i-methylene structures in an osmium carbonyl complex.

The n-system can be extended with methylene structures at the 3- and 5-positions. As expected, methyl groups at the 3,5-positions can be subjected to chemical modifications by the Knoevenagel reaction, owing to their acidic characteristics, generating styryl-bridged BODIPY derivatives by condensation with aromatic aldehydes (Scheme 7.5). " ... 

Trifonnals have been reported (241) and isolated in the case acids (242, 243). It may be that the methylol structure is the form obtained soon after the aldehyde and protein are mixed this changes with time to an irreversible methylene structure, evidence on this point has come to our attention. 

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