Alkenyl potassium

The two stereoisomeric 2-alkyl branched 2-alkenyl potassium species obtained upon deprotonation of ( )- and (Z)-isocaryophyllene equilibrate to afford an endo-exo... 

HomoaUyUc alcohols. Alkenyldimethoxyboranes add to aldehydes regioselec-tively to form homoallylic alcohols. The reaction is also diastereoselective (Z)-alkenylboranes react to form erythro-adducts, and (E)-alkenylboranes produce threo-adducts. The boranes are prepared by treatment of alkenyl potassium compounds with fluorodimethoxyborane (6, 261-262). 

A formal total synthesis of oximidine II was achieved by G.A. Molander et al., using an intramoiecuiar Suzuki-type cross-coupiing between an alkenyl potassium trifluoroborate and an alkenyl bromide to construct the highly strained, polyunsaturated 12-membered macrolactone core of the natural product. " The stability of potassium trifluoroborates was exploited in order to establish the best conditions for the macrocyclization. 

The Molander group reported a formal total synthesis of oximidine II, in which an intramolecular Suzuki cross coupling between an E-alkenyl potassium trifluoroborate and aZ,Z-dienyl bromide constructed the highly strained 12-membered macrolactone core of the natural product (Fig. 7) [22]. Importantly, the stereochemistry of the starting partners was conserved to deliver the ,Z,Z-conjugated triene in the natural product. 

With potassium /m-butoxide in tetrahydrofuran, the dibromodihydro-3//-l-benzazepines 7 (R1 = H, F, Cl) undergo syn dehydrobromination to synthetically useful alkenyl bromides, e.g. 8 (R1 = Cl), accompanied by small amounts of debrominated materials, e.g, 9 (R1 = Cl), and the 3-fcrf-butyl ethers, e.g. 10b(R1 = Cl, R2 = -Bu).78 In contrast, with sodium hydroxide, or with sodium methoxide in dioxane/methanol, the yields of bromo compounds 8 decrease, and significant amounts of the methyl ethers, e.g. 10a (R1 = Cl R2 = Me), arc produced. A mechanistic rationale for these reactions has been offered. 

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]. 

Knochel demonstrated the effectiveness of soluble potassium or cesium alkoxides such as KO Bu or CsO Bu as well as KH in iV-methylpyrrolidinone (NMP) for promoting the 5-endo-dig cyclizations of 2-alkynylanilines to 2-substituted indoles in solution or the solid-phase <00AG(E)2488>. Alternatively, Cacchi coupled a palladium-catalyzed cyclization of o-alkynyltrifluoroacetanilides with the addition of benzyl bromide or ethyl iodoacetate to afford 2-substituted-3-benzyl or 3-indolylcarboxylate esters, respectively <00SL394>. Yamamoto reported a new palladium catalyzed indole synthesis in which 2-(l-alkynyl)-Ar-alkylideneanilines 117 give 2-substituted-3-(l-alkenyl)indoles 118 directly from the imine by the in situ coupling of an aldehyde with the alkynylaniline <00JA5662>. 

Base-catalyzed leactions of hydrocarbons have been until recently limited to hydrocarbons having conjugated double bonds or double bonds that may be brought into conjugation, to alkenyl-aromatics, and to hydrocarbons possessing triple bonds ( ). Double-bond shifts of such compounds can occur at about 160° with such bases as alcoholic potassium hydroxide. 

It is a colorless liquid with an oily-fruity odor with floral, petal-like notes. For synthesis, 1,3-cyclohexanedione is reacted with crotyl bromide in the presence of potassium hydroxyde to give the 2-alkenyl-substituted 1,3-diketone. Ring cleavage with sodium hydroxyde leads to the unsaturated keto acid which is reduced with NaBH4 under formation of the title compound [201]. 

Reduction of a,P-unsaturated sulfones.1 Sodium amalgam (7, 326-327) is not satisfactory for reductive cleavage of alkenyl sulfones, R CH=CR2S02C6H5. These substrates are best reduced to alkcncs wth potassium-graphite (65-85% yields). 

Dienes react quite readily with alkylbenzenes to form monoalkenylbenzenes under controlled experimental conditions. Sodium and potassium deposited on calcium oxide were found to be very suitable catalysts for these alkenylation reactions.240 Naphthalene-sodium in tetrahydrofuran is a very effective catalyst... 

The outstanding chemical characteristic of alkenyl halides is their general inertness in SN1 and SN2 reactions. Thus chloroethene fails to react with silver nitrate in ethanol (i.e., low SN1 reactivity), fails to react with potassium iodide in acetone (i.e., low SN-2 reactivity), and only reacts slowly with sodium hydroxide to give ethyne (low E2 reactivity). The haloalkynes, such as RC=C—Cl, are similarly unreactive. 

The addition of Grignard reagents or organolithiums (alkenyl, alkyl, alkynyl, allyl or aryl) to nitroenamines (281)213 was reported by Severin to afford P-substituted-a-nitroalkenes.214 b Similarly, ketone enolates (sodium or potassium), ester enolates (lithium) and lactone enolates (lithium) react to afford acr-nitroethylidene salts (294) which, on hydrolysis with either silica gel or dilute acid, afford 7-keto-a,(3-unsaturated esters or ketones (295)2l4c-d or acylidene lactones (296).214 Alternatively, the salts (294, X s CH2) can be converted to -y-ketoketones (297) with ascorbic acid and copper catalyst. 

One organic group is readily transferred from tetraorganosilanes (and some other silanes) to palladium ). Tetramethylsilane, lithium tetrachloropalladate(II) and styrene at 120 C in acetonitrile solution form 1 -phenyl- 1-propene in 65% yield along with ca. 1.5% 2-phenyl-1-propene.33 Trimethylphenylsil-ane transfers phenyl and with styrene under the above conditions gives fra/w-stilbene in 94% yield.33 Similar vinyl substitution reactions have been achieved with potassium ( )-alkenyl pentafluorosili-cates.34... 

The Suzuki Coupling, which is the palladium-catalysed cross coupling between organoboronic acid and halides. Recent catalyst and methods developments have broadened the possible applications enormously, so that the scope of the reaction partners is not restricted to aryls, but includes alkyls, alkenyls and alkynyls. Potassium trifluoroborates and organoboranes or boronate esters may be used in place of boronic acids. Some pseudohalides (for example triflates) may also be used as coupling partners. 

Terminal attack occurs with water, methyl iodide, and trimethylchlorosilane, whereas central attack was preferred with alkenyl halides, aldehydes, and ketones at low temperatures under kinetic control [Eq. (5)]. The Et3SiO group is readily removed from 6 by potassium fluoride in isopropanol to give the vinyl ether RCH2CH2COCH=CH2 (61). Some of these reactions have also been used in elegant syntheses of terpenes (99-102). 

The substitution of alkenyl iodonium salts by halides, using tetrabutylammonium salts, has been studied (Table 9.2). Exclusive inversion of configuration occurred in acetonitrile, so that -precursors gave solely Z-haloalkenes in high yield [35]. In marked contrast, complete retention occurred with cuprous and potassium halides in dichloromethane. Retention of configuration was also noted in reactions of / -substituted alkenyl iodonium salts for example, from /J-phenylsulphonyl decenyl phenyliodonium ion, cis products were formed exclusively in high yield [34],... 

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