Methylene derivatives structure

In the case of the 2-dimethylamino- (or 2-amino-)methylene derivatives, the products were at first thought to be pyrimido[4,5-c]isoquinolines (267), but later work with 6-(N-substituted amino)uracils assigned the structures of the products (268) as belonging to the isomeric pyrimido[4,5-f>]quinoline system (74CB2537), in agreement with the regioselection rules above. 

Salvadori et al. [62] tested the same strategy but derived the bis(oxazohne) ligands in such a way that they minimized the steric hindrance at the bridging methylene carbon (structure 53 in Scheme 25). The polymer was used affording enantiomeric excesses superior to 90% and was reused at least five times with almost no loss in enantioselectivity or activity. 

In view of the activity of 13, but the lack of activity for the alpha-ethyl homolog of DOM, the two isomeric ring-methylated derivatives Structures 16a and 16b were recently prepared (114). Neither isomer showed significant activity, either as an agonist in the rat fundus preparation or in a mouse assay, when compared with 13. It would appear that little bulk can be tolerated near the alpha-carbon, other than a methyl or methylene. 

A further example of the diazaphosphole synthesis by [3 + 2] cycloaddition is given by the reaction of a phosphoranediyl diazomethane (26) (R = NPr j) with P-chloro-bis(trimethylsilyl)-phosphaethene. The adduct loses trimethylchlorosilane and yields a 3-phosphoranediyl-l,2,4-diazaphosphole (or 3-phosphonio-l,2,4-diazaphospholide) (27). The analogous addition to the trimethylsilyl substituted P-chloro-bis(methylene)phosphorane (28) yields a 4-methylene derivative (29) of this diazaphosphole (molecular structure in Table 1). It provides the only fully characterized example of this type up to 1995. Methyl triflate methylates the compound at N-1 and gives a phosphonio methylene diazaphosphole cation (30). 

In a logical continuation of this work, carbene addition to an iron-iron double bond has also been exploited for the simple synthesis of the first /. -methylene complex in the nitrosyl series. The readily available /x-nitrosyliron complex [(Tj5-C5H5)Fe(/u.-NO)]2 (26) exhibits the same structural features as the rhodium dimer 21 (157) and reacts with diazomethane in the temperature range -80-25°C to give the expected /z-methylene derivative 27 (Scheme 14) as a black, air-stable compound in... 

O.V. Shishkin, Molecular, electronic structure and conformational flexibility of the 1, 6-dihydropyrimidine, 4, 5-dihydrofuro[2, 3-d]pyrimidine and their oxo, imino and methylene derivatives. J. Mol. Struct. 385, 55-63 (1996)... 

Notable progress in the structural analysis of methylene derivatives of the polyhydric alcohols resulted from the investigations of Hann, Hudson and their co-workers26 80,40-4 into the behavior of these compounds during acetolysis. It was found that a mixture of acetic anhydride, acetic acid and 1-2% sulfuric acid ruptures preferentially any methylene bridge which spans a primary and a secondary position, giving the acetate ester of the primary hydroxyl and the acetoxymethyl ether of the secondary hydroxyl subsequent treatment with sodium methoxide removes each of these substituents. Under similar conditions, the acetolysis of a benzylidene compound results in the replacement of the arylidene residue, wherever it is located in the molecule, by two acetyl groups.16 29 47 48... 

H)-OxazoIones (78) are unstable with respect to the 4//-isomers (79) however, the 2-trifluoromethyl derivatives are unique in that the 2//-forms (78 R1 = CF3) are favoured (62LA(658)128). This was evident from the NMR spectra of numerous derivatives containing phenyl or alkyl groups at C(4) (64CB2023). While 2,2-disubstituted 5(2//)-oxazolones (80) have a fixed structure, the 2-methylene derivatives, such as 2-benzylidene-4-methyl-5(2H)-oxazolone (81), are in potential tautomeric equilibrium with 5(4//)-oxazolones, e.g. (82). However, compound (81) exists entirely in this form, no doubt because it is stabilized by conjugation of the phenyl group with the exocyclic double bond. 

Whereas strained ring systems are usually reactive and often unstable, molecules which satisfy the criteria for aromaticity exhibit enhanced stability. As is evident from the structural formula of 1, the cycloproparenes set these features in juxtaposition as they are strained molecules in which a single carbon atom is fused across adjacent centres of an aromatic system. The interest of the experimentalist in strained molecules has been matched by the theoretician in the search for suitable models for developing the concepts of chemical bonding and aromaticity. The cycloproparenes have been particularly important in this regard as they meet the criterion for partial aromatic bond localization and consequent bond length alternation in the aromatic ring as proposed by Mills and Nixon in 1930, viz. la vs lb. The cation 5, anion 6 and radical 7 derived from 1, and also the ketone 8 and exocyclic methylene derivative 9, are of interest in this respect. 

The expected reaction path leading to products 143 is not always followed, as it is affected by the substrate structure. In particular, a normal behavior is observed when n = 2, but when n = 3 further reaction with formaldehyde of the thiazolidine NH takes place to give N,N -bi.s-methylene derivative 150. When n= 1, the polycyclic product 149 is formed. 

The investigation of potential perfumery compounds from manool has continued with the preparation of some 12-methylene derivatives [e.g. (30)]. A relatively stable ozonide (31) has been obtained from manool. The crystal structure of the ruthenium tetroxide oxidation product (32) obtained from manool has been determined. The sulphur derivatives of the perfumery acetals obtained from manool have been prepared. ... 

The conformational flexibility postulated for the 2,4 3,5-diacetals of mannitol would disappear in acetals prepared from higher aldehydes and therefore possessing substituents at the acetal carbon atoms, but the status of such acetals is at present obscure., Two isomers of l,6-dichloro-l,6-dideoxy-2,3,4,5-di-O-ethylidene-D-mannitol are known, but the structures have not been determined. Two stereoisomers with the 2,4 3,5-structure and related to the H-inside and 0-inside conformations LVI and LVII, respectively, are clearly possible, but the structures 2,3 4,5 and 2,5 3,4 must also be considered. There is considerable scope for more work on 2,3,4,5-diacetals of mannitol, and confirmation of the structure XLVII advanced by Ness, Hann and Hudson for their mono-O-benzylidene-mono-O-methylene derivative is a necessary step in the assessment of the relative stability of the different structural types. 

Six-membered acetal rings fused to seven-membered rings are found in acetals formed directly from mannitol and certain of its derivatives. The 1,3 2,5 4,6-structure has been proved for the tri-O-methylene " and tri-0-ethylidene " derivatives of mannitol, and the 1,3 2,5-structure for the di-O-methylene derivative of 6-deoxy-L-mannitol. " These acetals are markedly more stable than the 2,4 3,5-diacetals discussed above. Their stability has been related to the probable mechanism of formation,"" but is also understandable on conformational grounds. " The ring junctions are trans, and the triacetals LXI have the trans-anti-trans configuration, which... 

Since its introduction early in this century, the deoxygenation of aldehydes and ketones to methyl or methylene derivatives, respectively, via base treatment of hydrazone intermediates (equation 1) has proven to be one of the most convenient and synthetically useful processes available for this important type of transformation. The reaction is termed the Wolff-Kishner reduction in recognition of the two original independent discoverers.However, the initial recipes introduced proved tedious and unreliable with many structural, especially hindered, examples. This led to substantial efforts devoted over the years to developing more convenient and successful experimental procedures, resulting in a number of improved and more reliable modifications which are most often utilized at present. More recently, modified procedures have been provided which utilize hydride reductions of p-toluenesulfonylhydrazone (to-sylhydrazone) derivatives and subsequent decomposition to release the hydrocarbon products under much milder and less basic conditions than those normally required for Wolff-Kishner reductions (equation 2). 

A number of more complex structures, useful in total syntheses, are accessible from olefins formed by Wittig olefinations of keto-sugars. A fmitful reaction is the dihydroxylation of double bonds. Obviously, methylene derivatives will give the hydroxymethyl branched-chain derivatives. 

A single-crystal X-ray structure determination revealed a constrained geometry of the bifunctional amide-cyclopentadienide ligand, that gives rise to the distortions in the metallocene geometry. The A-bonded methylene derived from a Cp methyl group is pulled out of the plane of the C5 ring toward the metal center by 0.52 A.123... 

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