3- Methyl-2-butenyl bromide

The reduction of 114 with LAH, followed by reaction with triphosgene, led to benzo[l, 2,5]thiadiazepin-6(4//)-one 1,1-dioxide 115, which upon treatment with Lawesson s reagent gave the corresponding thiocarbonyl derivative 116 (Scheme 26). The 1,2,5-thiadiazepine 115 was acylated by treatment with di-/-butyldicarbonate in the presence of AyV-dimethylaminopyridinc to afford 117, which is alkylated with 3-methyl-2-butenyl bromide or ethyl iodide to give 118 and 119, respectively <2002JHC81>. 

Configuration examination073 by H-nmr of the quaternary precursor of pentazocine (213a and b) and related compounds demonstrate that during quaternary salt formation, axial attack of the electrophile (from 3-methyl-2-butenyl bromide) occurs to yield predominantly 213b. This was consistent with earlier observations/174 175 An extensive study of the metazocines (base, HC1 salt, and methiodide) has been published,076 some results of which were later revised.077 178 ... 

This new alkylation procedure has been used for a simple synthesis of plastoquinune-1 (4) in 61 /o yield from 2,3-dimethylbenzoquinone and 3-methyl-2-butenyl bromide. Co-... 

Recently there has been interest in the synthesis of analogs of the naturally occurring mono- and diphosphate group. Corey and Volante ° have reported the alkylation of (dimethylphosphoryl)methyl-lithium with, for example, geranyl, famesyl and 3-methyl-2-butenyl bromides. Tlie products were assessed for their ability to inhibit the biosynthesis of squalene. McClard and coworkers described the alkylation of the phosphonylphosphinyl anion (14) to yield the P—C— P—C compounds, proven enzyme inhibitors (Scheme 13). The free acid derivatives were obtained by treatment of the alkylated products with bromotrimethylsilane. 

Also obtained by reaction of 3-methyl-2-butenyl bromide with pbloroacetopbenone in the presence of aqueous potassium hydroxide at r.t. for 24 h (29%) [4322],... 

The cyclopentane dione (0.154 g 5.58 x 10" mol) in dry ether (5 ml) is added to a vigorously stirred solution of sodium (0.3 g 1.3 x 10 mol) in dry ethanol (10 ml). After cooling to 0°C a solution of 3-methyl-2-butenyl bromide (0.075 g 5.03 x 10 mol) in ether (5 ml) is added. The mixture is stirred for 18 h, diluted with water, acidified (HCI) and extracted with ether. The ethereal layer is separated, washed with water, dried and concentrated in vacuo to an oil. Distillation yields 2-(3-methylbutanoyl)-5-(3-methyl-2-butenyl)-3,4-dihydroxy-4-(4-methyl-3-penten-1-ynyl)-2-cyclopentenone (0.084 g 44%) as a light-yellow oil with a boiling point of 100°C (bath temperature) at 5 X 10" mm Hg. 

Hulupone is synthesized in 54% yield by alkenylation of the sodium salt of dihydrohumulinic acid (see 8.4.3.1.1.) with 3-methyl-2-butenyl bromide (10). Cohulupone and adhulupone can be prepared similarly (9). However, cohulupone is more easily available from the natural colupulone. A series of analogous compounds has been obtained by reaction of dehydrohumulinic acid with various alkylating reagents (9,10). 

Upon boiling colupulone in methanol hydrogen chloride 12 N 10 3 during 3.5 h, two crystalline derivatives with molecular formula C20H28O4 s " obtained (1,2). The compound with a melting point of 83°C (190, Figs. 107 and 113) is synthesized by reaction of phlorisobutyrophenone with two equivalents of 3-methyl-2-butenyl bromide in dry chloroform (3). The neutral character of the tricyclic molecule is ascribed to the presence of an o.-hydroxyaryl ketone (4,5). Compound 190 can also be prepared by... 

To a suspension of phlorisobutyrophenone (3.25 g 1.66 x 10 mol) in chloroform (30 ml) is added 3-methyl-2-butenyl bromide (4.93 g 3.6 x lOr mol). Work-up involves dilution with chloroform (40 ml) and consecutive washings with sodium hydrogen carbonate, disodium carbonate and NaOH 1 N. The chloroform extracts are... 

Reaction of 2-methyl-2-butenyl bromide with lithiumtetramethylpiperidide in the presence of olefins furnishes (2-methyl-1-propenyl)cyclopropanes with moderate cis selectivity17. 

Tributyl(l-ethoxy-2-propenyl)stannane (2) was first prepared from tributyl[chloro(ethoxy)-methyl]stannane and vinylmagnesium bromide, and found to be unstable with respect to 1,3-migration of the tributyltin substituent101. Tributyl(l-ethoxy-3-methyl-2-butenyl)stannane (1) was found to be more stable, and has since been prepared directly from (tributyl)(diethoxy-methyl)stannane and 2-methylpropenylaluminum dichloride generated in situ102. 

Catalytic asymmetric methylation of 6,7-dichloro-5-methoxy-2-phenyl-l-indanone with methyl chloride in 50% sodium hydroxide/toluene using M-(p-trifluoro-methylbenzyDcinchoninium bromide as chiral phase transfer catalyst produces (S)-(+)-6,7-dichloro-5-methoxy-2-methyl-2--phenyl-l-indanone in 94% ee and 95% yield. Under similar conditions, via an asymmetric modification of the Robinson annulation enqploying 1,3-dichloro-2-butene (Wichterle reagent) as a methyl vinyl ketone surrogate, 6,7 dichloro-5-methoxy 2-propyl-l-indanone is alkylated to (S)-(+)-6,7-dichloro-2-(3-chloro-2-butenyl)-2,3 dihydroxy-5-methoxy-2-propyl-l-inden-l-one in 92% ee and 99% yield. Kinetic and mechanistic studies provide evidence for an intermediate dimeric catalyst species and subsequent formation of a tight ion pair between catalyst and substrate. 

The anions generated from tetracaibonyl(phosphine) carbene complexes are more reactive in their reactions with organic electrophiles. This is consistent with the observation that the p/iTa of the methyl pentacarbonyl complex (88a) is increased by six orders of magnitude when one of the carbon monoxi ligands is replaced with tributylphosphine. The anion generated fr-om (106) will give good yields of alkylated products with simple alkyl halides such as ethyl bromide however, dialkylation is still a serious side reaction. It has been reported that both pentacarbonyl and tetracarbonyl(phosphine) complexes can be efficiently monoalkylated with alkyl triflates (primary and secondary). The anion (89) for example, can be monoalkyated with the 3-butenyl triflate in 80% yield. ... 

Treatment of lV-methanesulfonyl-l,4-dihydFopyridine with n-butyllithium, followed by benzyl bromide, leads to the corresponding lV-l-(2-phenylethyl)sulfonyl-l,4-dihydropyridine in low yield. The sulfonamide shown in Scheme 131 (entry c) has proved a valuable c -isoprenoid synthon which allows the two-step C -homologation of allyl halides. This synthon was used for the remarkable two-step stereoselective synthesis of nerol from 3-methyl-2-butenyl chloride (Scheme 131, entry c). Finally, the a-chloro dicarbanion of 4-(a-chlon>methanesulfonyl)morpholine is readily availabl on reaction with 2 equiv. of n-butyllithium in THF, and it leads to the corresponding dimethyl derivative with no detectable monoalkylated product or starting sulfonamide on methylation. Intramolecular versions of these reactions allow the low yield synthesis of neopentyl cyclopropanesulfonate (scheme 131, entry d) and the efficient preparation of cyclopropanesulfomorpholine (scheme 131, entry e). ... 

An analogous rearrangement was observed with the preparation of l-benzyl-4,9-dihydro-4,6-dimethyl-7-(3-methyl-l -butenyl)-l //-imidazo[l, 2-a]purin-9-one (185a) by a three-step synthesis from 1-benzyl-4,9-dihydro-4,6-dimethyl-7-(hydroxy-methyl)-l//-imidazo[l,2-a]purin-9-one (183), which reacted with phosphorus tribromide to the corresponding 7-bromomethyl derivative 184a and with triphenylphosphine to the triphenylphosphonium bromide 184b. The latter reacted... 

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