3-methyl-1 -butene cycloaddition

Reactions of fluorinated dipolarophiles. Electron-deficient unsaturated species generally make better dipolarophiles, therefore, fluonnated alkenes become better dipolarophiles when vinylic fluonnes are replaced by perfluoroalkyl groups For example, perfluoro-2-butene is unreactive with diazomethane, but more highly substituted perfluoroalkenes, such as perfluoro-2-methyl-2-pentene, undergo cycloadditions in high yields [5] (equation 2) Note the regiospecificity that IS observed in this reaction... 

All of the butenes, pentenes, and hexenes were examined, taken in pairs. Methyl substituents increase the rates of cycloaddition, and different isoselective relationships... 

Following a report by Biichi and Ayer > on the photolysis of nitrobenzene in cyclohexene and 2-methyl-2-butene, a thorough study on nitrobenzene cycloaddition to olefines has been undertaken by de Mayo and co-workers 3 . ). Evidence was presented for the previously postulated ) formation of 1,3,2-dioxazolidines ... 

The experimental evidence most often employed to decide between the singlet and triplet multiplicity of a carbene is [1+2] cycloaddition to cis- or trans-olefins. The olefins employed in these studies are mostly 2-butenes or 4-methyl-2-pentenes, but in a few cases other olefins were also utilized. 

Photolysis of methyl-phenyl-diazomethane in cis-butene gives mainly styrene formed by hydride shift and the isomeric cycloaddition products 60—62 139) ... 

The cycloaddition of A-benzoyliminochloromethanesulfenyl chloride and 3,3-dimethyl-2-butene in nitromethane and in the presence of lithium perchlorate involves addition of the electrophile at the double bond and 1,2-methyl shift. Unusually, the ring closure is accompanied by elimination of the benzoyl group (Equation 16) <2002CHE1150>. 

N/L recorded was 16,000 for the reactions using the magnesium aUcoxide of 3-methyl-2-buten-l-ol as a multisubstituted internal allylic alcohol substrate, which is why regiocontrol is still effective in the reactions in a highly coordinating solvent such as THE. Rate enhancement is much lower in the nitrile oxide cycloaddition reactions using homoallylic alcohol substrates. 

The direct electrochemical oxidation of phenols generates phenoxonium cations which are able to undergo [3-1-2] cycloaddition in the presence of unactivated alkenes to produce benzofurans <1999JOC7654>. Thus, electrolysis of methyl 2,5-dihydroxybenzoate in a solution of lithium perchlorate in nitromethane in the presence of acetic acid and 2-methyl-2-butene produces the dihydrobenzofuran in excellent yield (Equation 88). 

Examples of this are the photocycloaddition reactions of 3-methylcyclohex-2-enone with ethene96 and isophoronc with l-propen-2-yl acetate.97 The cycloaddition of isophorone to methyl cyclobutene-1-carboxylate98 or of ( —)-piperitone (28) to 1,2-bis(trimethylsiloxy)cyclo-butene (29)99 affords tricyelo[4.4.0.02 5]deean-7-ones, used as starting compounds in fragmentation reactions. 

CYCLOADDITION Alumina chloride. l,2-Bis(trimethylsilyloxy)cyclo-butene. 2,2-Dimcthyl-3(2//)-furanone. Lthylaluminum dichloridc. Kctcnc diethyl acetal.. Methyl cyclobutene-carboxylate. Trimethyl-1,3-dioxolen-one. Zinc chloride. 

Regiospecific cycloaddition of 65 a, b, and c to furan has also been observed. None of the oxazolinones give photoadducts with other olefins, including methyl vinyl ether, cyclohexene, cis-2-butene, trans-2-butene, and styrene. 

Chromones are known to undergo [2+2] 71- and [3+2] 7i-photo-cycloadditions. Irradiation of 2-cyanochromone 311 in the presence of 2-methyl-2-butene produced both [2+2] 7t- and [3+2] 7i-cycloadducts (312 and 314 Scheme 42). Studies of this reaction under aerobic conditions have provided proof for the existence of iminium biradical 313 <1983TL2195>. 

Ene-additions of alkenes and dienes to silene 6 are considerably slower than [2 + 4]-cycloadditions. cA-Substitution in the ene component of the reaction causes a small acceleration in rate relative to fraws-substitution, as illustrated in Table 2 by the relative rate constants for reaction of 6 with cis- and rraws-2-butene. Reaction with cis, trans-2,4-hexadiene produces only a single adduct (66 equation 51), corresponding to selective ene-reaction with the cA-methyl group in the diene. 

In order to probe this phenomenon quantitatively in an uncharged system where solvation effects are known to be relatively unimportant, the rates of cycloadditions of two relatively electron-deficient 1,3-dipoles, p-methoxy and p-nitro benzonitrile oxides (MBNO and NMBO, respectively) to a series of simple alkenes — propene, 1-butene, 1-pentene, 1-hexene, 3-methyl-l-butene, 3,3-dimethyl-l-butene and isobutene — were measured70. In each of these reactions, only the 5-alkyl-3-aryliso-xazolines were formed. 

Photochemical cycloaddition of 2-arylisoindoline-l-thiones 8 to electron-poor alkenes 9, such as methacrylonitrile, 2-butene-2-nitrile and methyl methacrylate, affords the corresponding tricyclic isoindolines 10 as two diastereomers143. 

R and R may be H, methyl, cyclopropyl, cyano, or ester groups. The phenylcarbene formed on irradiation of trans-l,2-diphenyloxirane has been trapped and identified in the form of a cyclopropane derivative in methanol in the presence of benzyl methyl ether and alkenes. Photolysis in the presence of 2,3-dimethyl-2-butene proceeds by cycloaddition with the formation of cyclopropane-carboxylic acid and oxetane derivatives (Eq. 368). ... 

The N-metallated azomethine ylides having a wider synthetic potential are N-lithiated ylides 141, derived from the imines of a-amino esters, lithium bromide, and triethylamine, and 144 from the imines of a-aminonitriles and LDA (Section II,G). Ester-stabilized ylides 144 undergo regio- and endo-selective cycloadditions, at room temperature, to a wide variety of unsym-metrically substituted olefins bearing a carbonyl-activating substituent, such as methyl acrylate, crotonate, cinnamate, methacrylate, 3-buten-2-one, ( )-3-penten-2-one, ( )-4-phenyl-3-buten-2-one, and ( )-l-(p-tolyl)-3-phenyl-propenone, to give excellent yields of cycloadducts 142 (88JOC1384). 

A loganin aglucon synthesis has been developed as shown in Eq. 127 245>. Here the key step is the regioselective [3+2]-cycloaddition of 2-cyclopentenone and 3-[(tri-methylsilyl)methyl]-3-buten-2-ylmethylcarbonate. 

Disubstituicrtc Diazo-methane liefern 3H-Pyrazole1,78y 804-816 818-821 3diphenyl-methan und 3-Methyl-3-buten-l-in in 94% Ausbeute 3,3-Diphenyl-5-(l-methyl-ethenyl)-3H-pyr-... 

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