Cyclopropene dimethyl acetal

Hydrolysis of cyclopropene dimethyl acetal (45) provides a further useful route to cyclopropenone (equation 37). 

Density functional theory computational studies have been used to determine die importance of secondary orbital interactions for the stability of transition-state structures for die 4 + 2-cycloaddition of furan with cyclopropene.175 Kinetic studies of die 2 + 4-cycloaddition of 2-cyclopropylidene acetates with furan and dimethylful-vene suggest a mechanism involving diradicals or zwitterions as intermediates.176 Cyclopropene, produced by die reaction of allyl chloride with sodium bis(bimediyl-silyl)amide, reacts with 1,3-diphenylisobenzofuran to produce both endo- and exo-Diels-Alder cycloadducts isolated for the first tune.177... 

A number of cyclopropenes are available by routes which involve cyclopropanes as transient intermediates. For example, cyclopropenone dimethyl acetaF is obtained in yields up to 65% by sequential 1,3- and 1,2-elimination reactions (equation 24) the acetal... 

Bipyridine with [( j -cod)2Ni] in THF and further with dipheny-lacetylene gives [(jj -PhC = CPh)Ni(bipy)], which on the basis of structural data was described as the nickelacyclopropene 81 (01FJI77). Protonolysis with phosphoric or acetic acid gives cis-stilbene, whereas hydrochloric acid gives 82. Complex 81 catalyzes cyclotrimerization of alkynes. [( -cod)Ni(bipy)] reacts with dimethyl 3-methyl-3-f-butyl-l-cyclopropene-l,2-dicarboxylate to yield first the isolable intermediate 83, which was structurally characterized, and then complex 84 as the product (77JOM(135)405, 01OM1713). 

Enamines, Enol Acetates, Enol Ethers, and Vinyl Halides.—Diphenylcyclopropene-thione reacts with the morpholine enamines of cyclo-octanone and cyclododecanone to give adducts (337), which gave the strained cyclopropenes (338) when treated with dimethyl acetylenedicarboxylate. Other reactions of (337) have been reported." Whereas reactions of enamines with imidodialkylsulphonium chlorides usually give... 

Natural Cyclopropanes.—Ficini etal. have outlined a new approach to chrysaU themic acid ester (11) from commercially available 2,5-dimethyl-3-hexyn-2,5-diol, which has as a key stage the palladium-catalysed alkylation of the sulphone ester (10) with the acetate (9) (Scheme 3). cw-Chrysanthemic acid (14, R = H), is obtained by hydrogenation of the cyclopropene (13) produced by addition of diazopropane to the enyne (12). ... 

Cyclopropanation. Decomposition of dimethyl diazomalonate by direct photolysis or by transition metal catalysis in the presence of alkenes leads to cyclopropanation (eq 1). The use of alkynes to trap the carbenoid species affords cyclopropenes (eq 2). Rhodium(II) acetate-catalyzed reaction with allenes allows ready access to methylenecyclopropanes, which form the basis for a methylenecyclopentane annulation protocol (eq 3). ... 

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