Alkylidene derivatives compounds

However, benzylidene derivatives show a strong bathochromic shift in comparison with alkylidene derivatives. Thus absorption is a result of the whole conjugated system that is comparable to that of the quinoid dyes. The color of this type of compound is sensitive to acids and bases. 

Tertiary pyrrolines (49, = 1) and piperideines (49, = 2) (if R = H and the enamine can exist in the monomeric form or if R = aryl) evidently possess an endocyclic -double bond (79,155,156). The stretching frequency of the double bond can be lowered to 1620-1635 cm by conjugation with an aromatic substituent. The double bond of an analogous compound with aliphatic substituents in position 2 may occupy either the endo or the exo position. Lukes and co-workers (157) have shown that the majority of the five-membered-ring compounds, traditionally formulated with the double bond in a position, possess the structure of 2-alkylidene derivatives (50) with an exocyclic double bond, infrared absorption at 1627 cm . Only the 1,2-dimethyl derivative (51) is actually a J -pyrroline, absorbing at 1632 cm . For comparison, l,3,3-trimethyl-2-methylene pyrrolidine (52) with an unambiguous exocyclic double bond has been prepared (54). 

In the reaction of 2-isopropylidene-l-cyclopentanone 201 with carbon disulfide and ammonia, the perhydrocyclopenta[e][l,3]thiazine-2-thione derivative 204 was formed. The probable intermediates of the reaction are the Michael adduct 202 and the 2-imino-l-cyclopentanedithiocarbamic acid derivative 203. Under similar conditions, the related alkylidene derivatives gave the corresponding 3-substituted-2-imino-l-cyclopentanedithio-carbamic acid derivatives. Further substituted derivatives and homologs of 204 were also synthesized (74AKZ319), but the stereochemistry of these compounds was not investigated [73JCS(P1)1009]. 

S. Chltfdek and J. Smrt, Oligonucleotidic compounds. V. 2 ,3 -0-alkylidene derivatives of ribonucleosides, Colt Czech. Chem. Common. 26 1301 (1963). 

Most of the diorgano alkylidene tellurium compounds thus far reported derive their alkylidene group from 5,5-dimethyl-l,3-dioxocyclohexane. These diorgano cyclohexyl-idene tellurium compounds are colorless, crystalline substances that are stable at 20° and readily soluble in benzene, carbon tetrachloride, and dichloromethane2,3. Single crystal X-ray diffraction showed that the tellurium atom in bis[4-methoxyphenyl] 5,5-dimethyl-l,3-dioxo-2,2-cyclohexylidene tellurium occupies the apex of a trigonal pyramid4. 

Despite the paucity of data for 9 itself, there now exists a wide range of derivatives in the cyclopropabenzene and -[Z ]naphthalene series that have been expanded upon since a 1987 accountThe preparation of these derivatives can be effected by one of three distinct routes depending upon the particular nature of the compound sought. Each has its limitations and none has provided a parent methylenecycloproparene. The first method depends upon the availability of the cycloproparenyl anion (Section IV.B) which can be intercepted by trimethylsilyl chloride to give silane 93 (R=H). In turn, deprotonation of 93 at the benzylic position affords the stabilized a-silyl anion that gives alkylidene derivatives 94 (R=H) from interaction with an appropriate carbonyl compound in a Peterson olefination (Scheme 12). The reaction sequence can be effected as a one-pot operation... 

Peterson olefination involving cyclopropabenzenyl and cyclopropa[Z ]naphthalenyl anion intervention, respectively. Particularly noteworthy is the fact that subjection of disilyl-containing chromium(O) complexes (104, or its anthracene analogue) to r-BuOK provides C(i) anion without the loss of chromium in the case of 104 Peterson olefination has provided the corresponding complexed alkylidene derivative in high yield (equation 25) ", but the compound is unstable and decomposes upon attempted purification. 

W-Alkylidene derivatives of glycine esters are the preferred starting compounds for the synthesis of unnatural amino acids via the deprotonation/alkylation procedure. Enolate formation is achieved with a strong base (LDA, BuLi, or phosphazene bases such as 2- tert-butylimino)-2-(ethylamino)-l,3-dimethyl-l,3,2-diazaphosphinane) or by phase-transfer catalysis (tetraalkylammonium salts with NaOH or the latter method allows... 

Due to the hindered nature of the oxo group in these compounds the Wittig reaction is of limited use and a much more flexible route to the 4-alkylidene derivatives is through the 4-diazo and 4-thio compounds 22 and 23. 

Compound 11 forms 3-alkylidene derivatives (88) (Eq. 20)4,6 with benzal-dehyde and other aldehydes, including pyridine-2-carboxaldehyde. 

An interesting route to a-carboxy-8-lactones (81) and a-methylenelactones (80), based on hydrolysis of Knoevenagel products (79) of Meldrum s acid with cyclic aliphatic ketones (78), has been developed (Scheme 14). Reduction of 5-methylene derivatives of Meldrum s acid has been performed catalyti-caiiyi30 or by use of LAH. Imidoylation reaction of Meldrum s acid and subsequent solvolysis of the resulting (82) yields -enamino esters (83) in good yields.Flash vacuum pyrolysis of alkylidene derivatives of Meldrum s acid can be used to prepare methylene ketenes (84), a class of compounds difficult to prepare by conventional methods. By this procedure, methylene ketenes are obtained from aromatic aldehydes and ketones and from aliphatic ketones in only two steps. Intramolecular trapping of the methylene ketene obtained from the ketone (85) has been used successfully in the synthesis of the naphthol (86). ... 

Michael reactions. 2-Alkylidene derivatives of 1,3-dicarbonyl compounds behave as donors in Michael reactions. Of particular interest is the formation of biaryl precursors with quinones. ... 

Unlike Fischer-type compounds, alkylidene derivatives of niobium and tantalum have nucleophilic carbene carbon atoms. Therefore, they react with Lewis acids. 

The conversion of active-methylene compounds into 2-alkylidene derivatives of 1,3-dithiolans by base-catalysed condensation with carbon disulphide followed by treatment with 1,2-dihalogenoalkanes has been further exemplified, and extended to the synthesis of substituted alkyl-idene derivatives of 1,3-diselenolans and 1,3-diselenans. With dimethyl malonate, carbon diselenide, and either 1,2-dibromoethane or 1,3-dibromo-propane, for example, the compounds (142) and (143), respectively, were formed. Analogously, the dithiolate anion obtained from deoxybenzoin... 

B.i.b. Alkynes Containing Proximate 1,3-Dicarbonyl Groups. 2-Propargyl-1,3-dicarbonyl compounds react with alkenyl triflates or alkenyl/aryl/heteroaryl halides to give 2,3,5-trisubstituted-furans (Scheme 4). The process probably proceeds through an oxypalladation step that involves a nucleophilic attack of a stabilized enolate across the activated carbon-carbon triple bond, reductive elimination of a palladium(0) species from the resultant oxypalladation adduct, and isomerization of the initially formed alkylidene derivative. 

On treatment with a non-enolizable aldehyde and sodium hydride, rruns-related a-hydroxyepoxides were converted to acetals. The reaction is thought to proceed by way of a hemiacetal salt, as illustrated in Scheme 2. L-Galactono-1,4-lactone, a by-product of the sugar industry, furnished a diastereomeric mixture of 5,6-alkylidene acetals 18 in >60% yield on microwave irradiation in the presence of long-chain aldehydes and montmorillonite KSF as catalyst, and 4,6-O-alkylidene derivatives 19 of D-glucose have been prepared by use of long-chain aldehydes and catalytic pyridinium />-toluenesulfonate in benzene under azeotropic removal of water. Compounds 18 and 19 were of interest in liquid crystal studies. 

Another paper describes the reaction of some chlorobenzothiazinones (62) with triethyl phosphite that leads to the 2-phosphonates (63), from which a series of 2-alkylidene derivatives have been obtained by treatment with various carbonyl compounds, especially aromatic aldehydes. 

A study of the Michael addition of ester enolates R CH=C(OLi)OR to a-benzylidene and a-alkylidene -dicarbonyl compounds, for example, R CH=C(C02Me)2, has demonstrated that the diastereoselectivity depends on the substitution pattern of the Michael acceptor and the geometry of the enolate, which in turn can be controlled by the method of their generation (i.e. EDA in THF vs EDA and HMPA in THF). Thus, (E)-enolates exhibit iyn-diastereoselectivity, whereas (Z)-enolates afford the anti-diastereoisomers. Eow stereocontrol was observed with unsaturated nitriles and Meldrum s acid derivatives. A stereochemical model has been proposed to accounts for all experimental results. ... 

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