Cyclization -4,4-dimethyl-5-methylene

Carbanions in the form of ylides also add to azirines. For example, treatment of 1-azirine (227) with dimethylsulfonium methylide gives 1-azabicyclobutane (229) in good yield (72JA2758). The addition of the methylene group occurs by initial nucleophilic attack by the ylide to give intermediate (228) which cyclizes with expulsion of dimethyl sulfide. 

Carbanions of active methylene compounds also react with aziridine-2-car-boxylic esters to give ring-opened products [129]. The ring-opened intermediates usually cyclize spontaneously to pyrrolidones. Treatment of 190 (Scheme 3.70) with the sodium enolate of dimethyl malonate 191, for example, afforded pyrroli-done 192 in 15% isolated yield, together with 30% of the debenzoylated product 193. 

Replacement of one of the ethereal oxygen atoms by a methylene group is compatible with anticoccidial activity. For example, condensation of substituted aniline 35 with dimethyl ethoxymethylenemalonate affords aminoacrylate 36. Thermal cyclization in diphenyl ether gives neguinate (37).11... 

Active methylene nitriles condense with o-substituted aryl and heteroaryl azides in a two-step process to give tricyclic triazolopyrimidines without isolation of the triazole intermediates <85BSB441, 87BSB587). 5-Azido-4-formyltriazoles (758) condense with dimethyl 3-oxopentanedioate and tri-ethylamine in ethanol to give 5-(triazol-l-yl)-4-formyltriazoles (759), which undergo cyclization to... 

The chemistry of 5-methylene-2,2-dimethyl-l,3-dioxane derivatives in radical cyclizations (Equation 36, Section... 

Iodine-Mercury(II) oxide, 149 a-METHYLENE ALDEHYDES AND KETONES 1,4-Diazabicyclo[2.2.2]octane, 92 Dimethyl sulfoxide, 124 Formaldehyde, 136 Methoxyallene, 177 Methylene cycloalkanes By cyclization reactions Diacetatobis(triphenylphos-phine)palladium(II), 91 l-Hydroxy-3-trimethylsilylmethyl-3-butene, 147... 

Methylenecyclopentanes.2 Trost and Curran have used 1 as an electrophilic synthon for trimethylenemethane. Thus 1 reacts with the anion of 2 to give 3 in 72% yield. This product was oxidized to the disulfone, which was then cyclized to 4 by F. Various transformations are possible for the exocyclic methylene group. For the synthesis of coriolin (6), the group was converted to a pem-dimethyl group by cyclopropanation and hydrogenolysis. The product (5) was converted in several more steps into 6. 

Vicinally donor-acceptor-substituted olefins usually are rather unreactive species. Nevertheless cyclopropanation of 2,2-dimethyl-3(2 H)-furanone 70 could be executed with dimethyl oxosulfonium methylide as a methylene source. The bicyclic compound 71 is formed in modest yield accompanied by the spiro epoxide as a second product in almost equal amounts. Carbinols 72 derived from 71 by alkyl lithium addition can be nitrosated and photolyzed to suffer a Barton fragmentation. The resulting y-oxoaldehydes are directly cyclized to afford the 2-substituted cyclopentenones 73 in good yield 41. ... 

Spirooxindoles, such as, for example ( )-coerulescine (101) have been prepared employing a sequence starting from 2-fluoronitrobenzene, which was initially subjected to treatment with the anion of dimethyl malonate, followed by decarboxylation and concomitant installation of the methylene group using formaldehyde in the presence of potassium carbonate to produce the intermediate 102 in good yield. This material readily underwent dipolar cycloaddition with the azomethine ylide generated from sarcosine and formaldehyde, followed by a reductive cyclization of adduct 103 to furnish the natural product 101 <02TL9175>. 

Tellurophenes bearing substituents at the 2- and 5-positions were synthesized by first reacting sodium telluride with 4,4-dimethyl-3-chloropent-2-en-l-al. Addition of a chloro-methane derivative with an activated methylene group to the reaction mixture containing sodium l-fer/.-butyl-2-formyl-l-ethenetellurolate caused cyclization to 2-X-5-tert.-butyltellurophenes3. 

Indolo-steroids have been obtained by -coupling of steroid dienamines with dia-zonium salts in dimethylformamide followed by Fischer-indole cyclization of the resulting hydrazone39 (Scheme 37). In methylene chloride the /Fcoupled product 75 was obtained, cyclization of which gave indazoles 74 and 762a. The oxidative role of dimethyl sulphoxide in the formation of 76 was attributed to nucleophilic attack by the solvent on 75 leading to intermediates 77 and 78, with elimination of dimethyl sulphide (Scheme 38). 

The silylative coupling reaction of l,2-bis(dimethyIvinylsiloxy)ethane was effectively catalyzed by 1 mol% of ruthenium hydride catalyst, and the divinyl compound was completely consumed within 1 h at 80 °C. The reaction successfully proceeded without the solvent under air, but toluene could also be employed without affecting either the activity of the catalyst or the selectivity of this process. Application of this catalytic system for silylative coupling cyclization of l,2-bis(dimethyl-vinylsiloxy)ethane gave exclusively a cyclic product (Isolated yield 85%) with the exo-methylene bond between two silicon atoms in the molecule (2,2,4,4-tetramethyl-3-methylene-l,5-dioxa-2,4-dlsilacycloheptane) accompanied only by trace amounts of oligomers. 

The formal addition of a carbene to a C=S bond provides one possible route to the thiirane ring. An example is found in the synthesis of methylene-thiirane 411 by reaction of di-fert-butylthioketene with dimethyl diazomalo-nate in the presence of Rh2(OAc)4 (89TL1249). The interaction proceeds via an unstable thioketene 5-methylide 412, which undergoes 1,5-cyclization to the corresponding oxathiole at 50°C (Section VII,B,4), and at higher temperatures undergoes 1,3-cyclization to thiirane 411 (66%). 

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