Ethylidene derivatives

A/,A/-Dimethylamino)ethylidene Derivative, 234 a-(A/,A/-Dimethylamino)benzylidene Derivative, 234... 

As these acetals could be converted into the 4,6-O-ethylidene derivatives on treatment with acid, it was reasoned that use of a cyclic vinyl ether, namely, 3,4-dihydro-2H-pyran, might prevent this second process, thus leading to a more useful method of selective acetalation.338 An equimolar reaction with methyl a-D-glu-copyranoside for 4 days in N,N-dimethylformamide led to utilization of 88% of the glycoside, and the 6-(tetrahydropyran-2-yl) ether constituted —85% of the crude reaction-product. In contrast to the steric control apparent in this instance, reaction of 3,4-dihydro-2H-pyran with the axial and equatorial hydroxyl groups in dl-1,4,5,6-tetra-O-acetyl-mi/o-inositol was completely unselective,339 a fact that has been rationalized310 in terms of the probable mechanism of these reactions. 

The conversion of benzylidene and ethylidene derivatives into hydroxy benzoates and hydroxy acetates, respectively, following irradiation in acetone, and preferably in the presence of oxygen, was discussed by Binkley. Irradiation is carried out at a shorter wavelength (compared to 2-nitrobenzylidene derivatives) and the yields are significantly lower. 

When 2,2-disubstituted 1,3-dioxolanes were employed, mono- or poly-chlorination of the side chain was observed on the carbon atom a to the acetal grouping. Incidentally, it should be noted thatN-bromo-succinimide, N-chlorosuccinimide, and trichlorotetrahydrotriazine-trione were found to be effective for the preparation of bromoacetates from O-ethylidene derivatives this might be useful when O-benzyli-dene derivatives are not readily available, or when a problem arises due to the fact thatO-benzoyl groups are, in general, more difficult to remove than O-acetyl groups. 

Figure 5.101. It is apparent that stereochemistries in the 24-methyl, 24-ethyl, and 24-ethylidene derivatives could be controlled by the reduction processes or by proton loss as appropriate. It is more plausible for different stereochemistries in the 24-methyl and 24-ethyl side-chains to arise from reduction of different double bonds, rather than reduction of the same double bond in two different ways. In practice, other mechanisms involving a 25(26)-double bond are also found to operate.

Chemical Shifts of Some Ethvl, Vinylic, Acetylide, and Ethylidene Derivatives of Some Metals and Metalloids... 

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... 

The Wharton reaction has also been applied to the conversion of exocyclic a,p-epoxy ketones to the corresponding exocyclic hydroxy methylene products (Scheme 17). Similar conditions transform exocyclic methyl ketones into the exocyclic ethylidene derivative (Scheme 18). Not unexpectedly, the (Z)-alkene is isolated in only slightly higher yields than the ( )-isomer. 

Vinyl selenides, which behave similarly to vinyl sulfides, have also been prepared from ketones and reduced to the alkenic product. By this route, 3P-hydroxypregn-5-en-20-one was converted into the exo-cyclic 17-ethylidene derivative (Scheme 40). Vinyl selenides have also been reduced with NiB during... 

Of the many derivatives prepared, BRL 42715 (31) was the compound with the best overall activity and stability. The enzyme, renal dehydropeptidase I (RDHP) is known to be a major cause of metabolic inactivation of carbapenems, such as imipenem, and penems. Whereas the ethylidene derivative (90c) showed substantial degradation of the biologically active (5R)-enantiomer in the presence of human kidney homogenate, BRL 42715 proved particularly stable, with 68% surviving after I hour s exposure to human kidney [90,91], In addition, BRL 42715 was only moderately bound (68%) to human serum. 

Diols Both cis- and tran5-l,3-diols form cyclic acetals with aldehydes in the presence of an acid catalyst to furnish the corresponding benzylidene and ethylidene derivatives, respectively. 

In the presence of catalytic amounts of p-toluenesulfonic acid, D-galactose diethyl dithioacetal (112) reacts248 with tert-butyl vinyl ether to afford the 5,6-O-ethylidene derivative 113 in 56% yield Wolfram and Parekh248 proposed that the reaction proceeds by initial, electrophilic addition of 0-6 to the double bond, followed by pro-... 

Dimethoxyethylidene, 349 a-Methoxybenzylidene, 349 l-(A,A-Dimethylamino)ethylidene Derivative, 349 (X-(A,A-Dimethylamino) benzylidene Derivative, 349 Butane-2,3-bisacetal, 350 Cyclohexane-1,2-diacetal, 351 Dispiroketals, 352... 

V,(V-Dimethylamino)ethylidene Derivative a-((V,A -Dimethylamino)henzylidene Derivative ... 

The 3-methyl ethers of the 4,6-0-benzylidene and 4,6-0-ethylidene derivatives of methyl 2-(A-benzyloxycarbonyl)amino-2-deoxy-a-n-gluco-pyranoside have been prepared by a sequence of reactions paralleling Neuberger s synthesis. The d anomer of the latter compound was obtained directly by methylation of 2-(A-benzyloxycarbonyl)amino-2-deoxy-4,6-0-ethylidene-D-glucose with dimethyl sulfate and alkali. Both anomers were transformed into the free amines by catalytic hydrogenolysis. ... 

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