Conjugate substitution alkenylation

Palladium catalysed conjugate substitution via alkyl-alkenyl coupling preparation of 4-[( )-4-methyl-3-nonenyl]-2(5H)-furanone35a... 

Pd-catalyzed conjugate substitution, as defined in Scheme 1 of Sect. III.2.15, is nothing more than Pd-catalyzed alkenylation with /3-halo- or /3-metallo-substituted a,/3-unsaturated carbonyl compounds and related derivatives. Since the reaction is closely related to the widely known conjugate addition and since it can serve as the component of a novel and alternative conjugate addition protocol, their special discussion is warranted. 

Pr)4, " borohydride-exchange resin,and formic acid. When the last is used, the process is called the Wallach reaction. Conjugated aldehydes are converted to alkenyl-amines with the amine/silica gel followed by reduction with zinc borohydride.In the particular case where primary or secondary amines are reductively methylated with formaldehyde and formic acid, the method is called the Esch-weiler-Clarke procedure. It is possible to use ammonium (or amine) salts of formic acid, " or formamides, as a substitute for the Wallach conditions. This method is called the Leuckart reaction,and in this case the products obtained are often the N-formyl derivatives of the amines instead of the free amines. Primary and secondary amines can be iV-ethylated (e.g., ArNHR ArNREt) by treatment with NaBH4 in acetic acid. Aldehydes react with aniline in the presence of Mont-morillonite KIO clay and microwaves to give the amine. Formaldehyde with formic acid converts secondary amines to the N-methyl derivative with microwave irradiation. 

Alkenyl Fischer carbene complexes can serve as three-carbon components in the [6 + 3]-reactions of vinylchro-mium carbenes and fulvenes (Equations (23)—(25)), providing rapid access to indanone and indene structures.132 This reaction tolerates substitution of the fulvene, but the carbene complex requires extended conjugation to a carbonyl or aromatic ring. This reaction is proposed to be initiated by 1,2-addition of the electron-rich fulvene to the chromium carbene followed by a 1,2-shift of the chromium with simultaneous ring closure. Reductive elimination of the chromium metal and elimination/isomerization gives the products (Scheme 41). 

Unfortunately, this process gave good results only with bulky substituents at the acetylenic terminus in 104 and, surprisingly, Jeffery s conditions—but without a quaternary ammonium salt—were found to work best. With an additional alkenyl substituent at the acetylenic terminus as in the cyclohexenyl-substituted 2-bromonona-l,8-dien-6-yne 109, the co-cyclization with bicyclopropylidene 12, under these conditions, leads to 110. This transformation involves two consecutive 67r-electrocyclizations of the initially formed cross-conjugated pentaene 111, which was not isolated (Scheme 30). ... 

A variety of geminally substituted cyclopropyl ethers are synthesized employing Fischer carbene complexes [(CO)5M=CR (OR2) M = Cr, Mo, W R1 = alkyl, alkenyl and aryl] as alkoxycarbene sources. Electron-deficient alkenes and conjugated dienes are suitable substrates for the reaction (equation 108)237-245. Electron-rich enol ethers and enamines are also... 

Ruthenium(O) complexes such as Ru(COD)(COT) catalyze the dehydrohalo-genative coupling of vinyl halides with olefins to give substituted conjugated dienes in a Heck-type reaction [11]. Thus, alkenyl halides readily react with activated olefins to produce dienes 16 (Eq. 7). Oxidative addition of vinyl halide, followed by regioselective insertion of an electron-deficient olefin and by -hydrogen elimination leads to the diene. 

Another type of intramolecular electrophilic substitution is shown in Equation (1).25 In this case, the reaction sites are located in different substituents on silicon. This reaction mode is useful for highly diastereoselective alkenylation and phenylation of aminoacetals and hemiaminals.26 Intramolecular conjugative arylation of a-enals bearing an aryldimethylsilyl group is effectively promoted by tetrabutylammonium fluoride (TBAF) (Equation (2)).27,27a... 

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