Alkenyl fluorides

Chlorobenzenes activated by coordination of Cr(CO)3 react with terminal alkynes[253). The 1-bromo-1,2-alkadiene 346 reacts with a terminal alkyne to afford the alka-l,2-dien-4-yne 347[254], Enol tritlates are used for the coupling with terminal alkynes. Formation of 348 in the syntheses of ginkgolide[255] and of vitamin D are examples[256] Aryl and alkenyl fluorides are inert. Only bromide or iodide is attacked when the fluoroiodoalkene 349 or fluoroiodoar-ene is subjected to the Pd-catalyzed coupling with alkynes[257-259]. 

A novel method for the convenient synthesis of alkenyl fluorides 15, as well as diflu-oromethyl-substituted alcohols 16 and amides 17, via electrophilic fluorination with one equivalent of F-Teda BF4 (6) of alkenyl boronic acids and trifluoroborates, has been reported.87 The alkenyl fluorides 15 are obtained as Z/E mixtures when the reaction is carried out with one equivalent of F-Teda BF4 in acetonitrile at room temperature. When the reaction is performed with two equivalents of F-Teda BF4 in water or a nitrile solvent the difluoromethyl-substituted alcohols 16 or amides 17, respectively, are obtained. 

Alkenyl fluorides.1 Alkenyllithium compounds, obtained from reaction of alkenyl iodides with J-butyllithium, are converted into alkenyl fluorides by reaction with an N-f-butyl-N-fluorobenzenesulfonamide (1) in THF/ether/pentane at -120 - 20° yields 71-88%. 

The reactions take place under mild conditions with good to high yields. Another important advantage is the use of relatively nontoxic reagents. In the synthesis of the alkenyl fluorides, mixtures of Z/E isomers are obtained. The substrate trifluoroborates can be prepared from the corresponding boronic acids by reaction with potassium hydrogen fluoride/water. ... 

Allylic oxidation. Recycling of SeOj with r-BuOOH in situ is an old technique, and its extension to the oxidation of alkenyl fluorides is routine. The same reagent combination on silica under microwave irradiation shortens the reaction time for the allylic oxidation. ... 

Alkenyl fluorides. These compounds can be prepared from alkenylstannanes by... 

The reaction has also been used in the preparation of a-fluorocarboxyhc acids with good enantioselectivity, including the conversion of the alkenyl fluoride (2.79) into a-fluorohexanoic acid (2.80). ... 

Thus, the optimized carbometallation reaction of propargylic alcohols with aromatic Grignard reagents proceeds without an additional metal catalyst and leads to the formation of an alkenyl fluoride. The stereoselective defluorometallation proceeds to form predominantly the fluorinated (Z)-carbon-carbon double bond in the final allene 276. Two reasons were proposed by the authors for such a high level of stereoselectivity the defluorometallation is favored from the intermediate... 

Tin enolates of ketones can be generated by the reaction of the enol acetate 733 with tributyltin methoxide[60i] and they react with alkenyl halides via transmetallation to give 734. This reaction offers a useful method for the introduction of an aryl or alkenyl group at the o-carbon of ketones[602]. Tin enolates are also generated by the reaction of siiyl enol ethers with tributyltin fluoride and used for coupling with halides[603]. 

A trialkylsilyl group can be introduced into aryl or alkenyl groups using hexaalkyidisilanes. The Si—Si bond is cleaved with a Pd catalyst, and trans-metallation and reductive elimination afford the silylated products. In this way, 1,2-bis-silylethylene 761 is prepared from 1,2-dichloroethylene (760)[625,626], The facile reaction of (Me3Si)2 to give 762 proceeds at room temperature in the presence of fluoride anion[627]. Alkenyl- and arylsilanes are prepared by the reaction of (Me3Si)3Al (763)[628],... 

Organolithium reagents (Section 14 3) Lithi um metal reacts with organic halides to pro duce organolithium compounds The organic halide may be alkyl alkenyl or aryl Iodides react most and fluorides least readily bro mides are used most often Suitable solvents include hexane diethyl ether and tetrahy drofuran... 

The original conditions used amines as solvents or cosolvents. Several other bases can replace the amine. Tetrabutylammonium hydroxide or fluoride can be used in THF (see Entry 1 in Scheme 8.11).163 Tetrabutylammonium acetate is also effective with aryl iodides and EWG-substituted aryl bromides (Entry 2).164 Use of alkenyl halides in this reaction has proven to be an effective method for the synthesis of enynes165 (see also Entries 5 and 6 in Scheme 8.11). 

In 1998, Harmata and co-workers <98T9995> published a new synthesis of 2-alkenyl anilines. The silylated 2,1-benzothiazines 187 could be deprotonated by n-BuLi and alkylated by different electrophiles. The corresponding products could be desilylated by fluoride with concomitant cleavage of the carbon-sulfur bond to give 2-alkenylsulfinanilides that can then be hydrolyzed by base to the anilines 195 in good yields (Scheme 55). 

In general, the syntheses of these complexes are achieved through (i) nucleophilic addition/substitution reactions of silver(i) fluoride or (ii) transmetallation reactions with other metal alkyl, alkenyl, and aryl complexes. 

A rapid MW-assisted palladium-catalyzed coupling of heteroaryl and aryl boronic acids with iodo- and bromo-substituted benzoic acids, anchored on TentaGel has been achieved [174]. An environmentally friendly Suzuki cross-coupling reaction has been developed that uses polyethylene glycol (PEG) as the reaction medium and palladium chloride as a catalyst [175]. A solventless Suzuki coupling has also been reported on palladium-doped alumina in the presence of potassium fluoride as a base [176], This approach has been extended to Sonogashira coupling reaction wherein terminal alkynes couple readily with aryl or alkenyl iodides on palladium-doped alumina in the presence of triphenylphosphine and cuprous iodide (Scheme 6.52) [177]. 

Optimum yields of (3-vinyl-y-butyrolactols from the Pd(II) promoted reaction of vinyl triflates with Z-but-2-en-l,4-diol (Scheme 6.33) are attained when tetra-n-butylammonium chloride is added (47]. The lactol is conveniently oxidized to the lactone with celite-supported silver carbonate. The corresponding arylbutyrolactols are obtained in high yield (70-80%) from an analogous reaction of iodoarenes with the enediol. The yields of 2-alkenyl-2,5-dihydrofurans, resulting from the Pd(0) catalysed reaction of cyclic alkynylcarbonates with acrylic esters via tandem C-C and C-0 bond forming reactions, are enhanced by the presence of tetra-n-butyl-ammonium fluoride (e.g. Scheme 6.33) (48]. 

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