3- Methylpent-2-ene

From the reaction mixture of 2-aminopyridine and perfluoro-2-methylpent-2-ene in MeCN a 9 1 mixture of 2,4-difluoro-2-penta-fluoroethyl-3-trifluoromethyl-4//- and isomeric 2,4-difluoro-4-penta-fluoroethyl-3-trifluoromethyl-2//-pyrido[l, 2-a]pyrimidine (64%), and 2-pentafluoroethyl-3-trifluoromethyl-4//-pyrido[l,2-a]pyrimidine-4-one (20%) was isolated (00JFC105). 

Reaction tests The 2-methylpent-2-ene (2MP2) isomerization test was carried out as... 

Amines, thiols, eOH (p. 226), etc., will also add to the 0-carbon atom of 0-unsaturated carbonyl compounds and esters, but the most important reactions of C=C—C=0 systems are in Michael reactions with carbanions reactions in which carbon-carbon bonds are formed. A good example is the synthesis of l,l-dimethylcyclohexan-3,5-dione (dimedone, 100) starting from 2-methylpent-2-ene-4-one (mesityl oxide, 101) and the carbanion 0CH(CO2Et)2 ... 

Cyclocondensation of 2-iminopiperidine and 3-aryl-2-propynylnitriles afforded 4-aryl-2-imino-6,7,8,9-tetrahydro-22/-pyrido[l,2- ]pyrimidines <20000L3389, 2002W002/00629>. The minor isomers, 2-aryl-4-imino-6,7,8,9-tetrahy-dro-4/7-pyrido[l,2- ]pyrimidines could also be isolated in 2-30% yields from the reaction mixtures <20000L3389>. When the reactions were carried out in the presence of 2 equiv of NaHMDS, the product ratio was reversed. From the reaction mixture of 2-aminopyridine and perfluoro-2-methylpent-2-ene in MeCN, a 9 1 mixture of 2,4-difluoro-2-pentafluoroethyl-3-trifluoromethyl-477- and the isomeric 2,4-difluoro-4-pentafluoroethyl-3-trifluoromethyl-277-pyr-ido[l,2- ]pyrimidine (64%), and 2-pentafluoroethyl-3-trifluoromethyl-47/-pyrido[l,2- ]-pyrimidine-4-one (20%) was isolated <2000JFC(103)105>. 

The 1,2-hydrosilylation of a,/3-unsaturated ketones is possible and provides a convenient route to allyl alcohols. The standard conditions of Et3SiH/TFA lead to overreduction to the saturated alcohol with mesityl oxide 434,439 The combination of EtsSiH/AlCE/HCl with mesityl oxide gives a mixture of the 1,2-reduction product 4-methylbut-3-ene-2-ol and the fully reduced product, 2-methylpent-2-ene.136 The Ph2SiH2/RhH(PPh3)4 reduction of cyclohexenone gives reaction at... 

Fluorinated azetines 1 and 2 are obtained by treatment of perfluoro-2-methylpent-2-ene with heteroaromatic amines (e.g. 6-bromobenzothiazole) and with the more nucleophilic aliphatic amines (e.g. isopropylamine), respectively <00MI99>. 

Two approaches have been applied for the synthesis of imidazo[2,l + thia/,ole ring systems. Reaction of 2-mercapto-benzimidazole with perfluoro-2-methylpent-2-ene in the presence of triethylamine gave compound 419 (Equation 192), and cyclocondensation of 2-imidazolidinethione with the alkynyl(phenyl)iodonium salt 420 afforded product 421 (Equation 193) <2001RCB1446, 2003JCM715>. 

A complex reaction between perfluoro 2-methylpent-2-ene and carboxylic acids in the presence of potassium carbonate and Aliquat produces the acid fluoride, as the major product, with variable amounts of the 3-acyloxy perfluorinated alkene [37]. The procedure has little value for the synthesis of either compound. 

The reaction between 2-aminopyridine and 2-amino-4-methylpyridine with perfluoro-2-methylpent-2-ene gave pyrido[l,2-a]pyrimidines, but 2-amino-6-methylpyridine gave the naphthyridine (220) (74CC134). 

The acidic form of sodium fluoride, sodium bifluoride is scarcely used for introduction of fluorine in organic compounds. One reported example is the addition of bromofluorine to perfluoro(2-methylpent-2-ene) (20) generated by reacting A V -dibromodimethylhydantoin with acidic sodium fluoride in the presence of tetrabutylammonium hydrogen difluoride at 0°C to give 21.20... 

In the presence of freeze-dried potassium fluoride, perfluoro-2-methylpent-2-ene reacts with activated methylene compounds to yield pyrans (81MI22400). The fluoride ion abstracts a proton from the methylene group and subsequent condensation of the carbanion with the perfluoroalkene affords a dienone (19) which ring closes to the pyran (20 Scheme 3). In the case of pentane-2,4-dione a divinyl ether (21) is also formed. This product is considered to arise from reaction of the alkene at the oxygen of the enolate ion. 

A patent assigned to Central Glass describes the rearrangement of internal perfluoroalkenes with potassium fluoride and a crown ether in acetonitrile. For example, periluoro(4-methylpent-2-ene) (7) can rearrange to the more stable isomer perfluoro(2-methylpent-2-ene) (8) by heating for 3 hours at 40 C in acetonitrile in the presence of catalytic amounts of potassium fluoride and 18-crown-6.32... 

The course of addition reactions of ROH-XeF2 to alkenes has been elucidated using norbomene, 2-methylpent-2-ene and hex-l-ene as model substrates. It turned out that the alkoxyxenon fluoride intermediates (ROXeF) can react either as oxygen electrophiles (initially adding alkoxy substituent) or as apparent fluorine electrophiles (initially adding fluorine), depending on the reaction conditions. Simple addition of poorly nucleophilic alcohols to norbomene was also observed in certain instances. Selectivity between the various reaction pathways (simple fluorination, alkoxyfluorina-tion, or alcohol addition) proved to be sensitive to various reactions conditions, especially solvent, temperature, and catalyst.27... 

The reaction of perfluoro-2-methylpent-2-ene 641 with 2-amino-6-bromobenzothiazole 642 and with more nucleophilic isopropyl amine 643 afforded 2-azetines 644 (Equation 244) and 645 (Equation 245), respectively <2000RJ099>. 

Second, intramolecular cyclization involving the azido group and the double bond could yield 1,2,3-triazoline derivatives these may be thermally unstable and may undergo nitrogen elimination to afford azirine derivatives. The reaction of perfluoro-2-methylpent-2-ene with NaN3 in a 1 2 acetonitrile-ethanol mixture at — 10°C (2 h) yielded stable 5-ethoxy-5-pentafhioroethyl-4,4-bis(trifluoromethyl)-4,5-dihydro-1H-1,2,3-triazole 9, whose structure was confirmed by X-ray analysis, Fig. 1 (01 JFC(110)21, 97ZOR772). 

The reaction of hexamethyldisilazane with the adduct of perfluoro-2-methylpent-2-ene and triethylamine yields perfhioro-3-methyl-4-ethylazete and perfhioro-2-methyl-3-ethylazetine, the former being predominant (98ZOR42). 

Thus isomerization of perfluoro-2-methylpent-2-ene can give perfluoro-2-methyl-l-pent-l-ene. The terminal multiple bond of the latter is rather labile with respect to the nucleophilic reagents. This can change the reaction... 

These results clearly demonstrate the importance of steric factors in reactions of perfluoro-2-methylpent-2-ene with primary alkylamines. 

When perfluoro-2-methylpent-2-ene reacts with glycidol, the initially formed product is vinyl ether 38, whose epoxide ring opens under the action of mineral acids (8% HBr, 33% HC1). Alcohol 39 formed in the course of ring cleavage is readily cyclized into 1,3-dioxolane 40 in the presence of catalytic amounts of NEt3. 

The interaction of perfluoro-2-methylpent-2-ene and epichlorohydrin in the presence of CsF or triethylamine in aprotic solvents forms tetrahydrofuran 49. The reaction occurs by cleavage of the epoxide ring under the action of the fluoride ion generating an O-nucleophilic center, which reacts at the multiple bond of the perfluoroolefin. Further cyclization the new terminal double bond gives the final reaction product. 

Table II. Dependence of the Ratio of the Products of the Reaction between Perfluoro-2-methylpent-2-ene and Ethylene Glycol in the Presence of NEt3 in Various Solvents (85IZV2066)...

It was shown (78JFC(12)193) that the product of the reaction of perfhioro-2-methylpent-2-ene with potassium ethyldithiocarbamate in dimethylformamide is 5,5-bis(trifhioromethyl)-5-(tetrafluoroethylidene)-2-fhioro-2-ethoxy-l,3-dithiolane. Analogously, the reaction of 1,1,1-trifluoro-methyl-2-bromoprop-2-ene with thiourea and its N-substituted derivatives yields 5-trifhioromethyl-2-thione-thiazolidines 57 (92JFC(58)365). 

Table IV. Products of the Reaction of Perfluoro-2-methylpent-2-ene with Binucleophiles...

Based on the assumptions about the reaction mechanism, one can predict that this technique will be applicable to other binucleophiles for the synthesis of perfluoroalkylated heterocyclic compounds. For example, the reaction of arylhydrazine with perfluoro-2-methylpent-2-ene in the presence of triethylamine led to N-arylperfluoro-3-ethyl-4-methylpyrazole 58 and N-arylperfluoro-4-methyl-5-ethylpyrazole 59 in different ratios depending on the reaction conditions (89RP1456419, 87RP1456418, 90IZY2583 89JAP(K)01 22855 99JFC(98)29). Syn- and /-aminoimines are intermediates in syntheses of pyrazoles they were isolated individually. On heating in the presence of triethylamine they are transformed into mixtures of 58 and 59. 

Polyfluorinated arylhydrazines proved to be sufficiently active nucleophilic reagents in reactions with perfluoro-2-methylpent-2-ene, giving fluorine-containing pyrazoles. 

At the same time, the interaction between perfluoro-2-methylpent-2-ene and hydrazine hydrate under the same conditions leads to the formation of the imine of the corresponding ketones 60 and 61. 

In the case of the reaction of perfluoro-2-methylpent-2-ene with 1,1-dimeth-ylhydrazine in the presence of triethylamine as the dehydrofluorinating agent and Et20 as a solvent at —50 to 0°C, the product is 5,5-difluoro-l,l-dimethyl-3-pentafhioroethyl-4-trifluoromethyl-1 -pyrazolin-2-yl 64 (87RP14 56418, 90IZY2583). 

It was found (91JFC(54)221) that the product of interaction between perfluoro-4-methylpent-2-ene and pyrrolidine is 4-pyrrolidineperfluoro-2-methylpent-2-ene 74. On storage in the absence of bases it is converted into 2,4,4-tns-(trifhioromethyl)-3-fluoro-l-azabicyclo-[3.3.0]oct-2-ene 75. The formation of compound 75 may be explained as follows. The mobile... 

Another interesting process was found (94IZV1068, 94IZV1073, 94IZV1449). Investigation of the reaction of perfhioro-2-methylpent-2-ene with acetone oxime showed that the acetone oxime ether 3-perfluoro-2-methylpent-2-en-2-yl 83 formed initially reacts at 100 °C for 1 h, giving 4-hydroxy-3-methyl-5,5-bis(trifluoromethyl)-4-pentafluoroethylpyrrolone-l 84 in quantitative yield the structure of this product was confirmed by X-ray analysis. 

This reaction is probably of general character. Thus the reaction of cyclopentanone and cyclohexanone oximes with perfluoro-2-methylpent-2-ene forms perfluoroalkenyl ethers. Thermolysis of the latter leads to... 

Thus reactions of perfluoro-2-methylpent-2-ene and perfluoro-5-azanon-4-ene with urea in the presence of triethylamine in dipolar aprotic solvents (MeCN, DMF) form 6-fluoro-4-pentafluoroethyl-5-trifluoro-methyl-l//-pyrimidin-2-one 93 and an s-triazine derivative, respectively (00JFC(103)105, 80/82JAP(K)85377). 

The reaction of perfluoro-2-methylpent-2-ene with benzamidines in the presence of sodium hydroxide affords 4-fluoro-2-phenyl-6-pentafluoro-ethyl-5-trifhioromethylpyrimidine 95 (00JFC(103)105). In compound 95, the fluorine atom in the 5 position possesses high mobility in a... 

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