4- Methylene-l,3-dioxolanes

Dimethyl-4-methylene-l,3-dioxolan-2-one reacts with isonitriles in the presence of a palladium catalyst to afford iminofurans (Equation (121)).480 Successive insertion of isonitriles to the carbon-palladium bond of 7r-allylpalladium intermediate is postulated. 

Studies on the polymerization of various 4-methylene-l,3-dioxolans [94] by BF3Et20 or A1C13 showed that 4-methylene-l,3-dioxolan itself polymerises mainly through the double bond the 2-methyl and 2,2-dimethyl compounds gave polymers with a variable carbonyl content. This arises from a co-polymerization in which units of type (VII) and (VIII) are incorporated in the chain in different proportions, according to the reaction conditions ... 

A very special type of template polymerization was presented by a group of Japanese scientists. The method used was based on the observation that during radical polymerization of 2,2-diphenyl-4-methylene-l,3-dioxolane, elimination of benzophe-none occurs according to reaction ... 

Reduction of a,a -dibromo ketones. Reduction of 2,4-dibromo-2,4-dimethyl-pentane-3-one (1) with ultrasonically dispersed mercury in the presence of a ketone such as acetone leads to a 4-methylene-l,3-dioxolane (2) in about 50% yield. A similar reaction has been observed in the reduction of dibromo ketones with zinc in dimethylformamide (5, 221). 2-Oxyallyl cations such as a have been invoked as intermediates in reductions of dihalo ketones with various metals. 

Lithium allenolates are obtained from 2,2-dimethyl-4-methylene-l,3-dioxolane and 2 equiv. of r-bu-tyllithium. These allenolates can further undergo aldol reactions (Scheme 21). ... 

The reaction of epichlorohydrin with hexafluoroacetone in the presence of catalytic amounts of Bu4NBr affords 2,2-bis(trifluoromethyl)-4(bromomethyl)-l,3-dioxolane 16, which on further treatment with KOH yields 2,2-bis(trifluoromethyl)-4-methylene-l,3-dioxolane 17 (92JPK311) (Scheme 19). 

The radical ring-opening elimination polymerization of 4-methylene-l,3-dioxolane stimulated us to construct a novel template polymerization (3). The concept is that polymers bear polymers. Polymer-supported monomer, which had a structure of 2,2-dipheny 1-4-methylene-1,3-dioxolane, reacted with radical species to afford polyketone and copolymer of styrene with vinylbenzophenone as newborn polymer and template, respectively (Figure 12). These polymers were easily separated by fractional precipitation without any particular chemical treatment after polymerization. On the other hand, common template polymerization requires annoying procedures for the separation of obtained polymers form template. On this point, our novel template polymerization system differs from conventional template polymerization. 

Beside carbenes and carbenoids, metal-catalyzed cyclopropanation using other types of intermediate is also feasible. Treatment of 5-methyl-5-phenyl-4-methylene-l,3-dioxolan-2-one with palladium(O) catalyst in the presence of norbomene produced the cyclopropyl ketone in excellent yield (Scheme 8) (60). The active intermediate was proposed to be a Zwitterion... 

Sugiyama and co-workers (69,70) report a very interesting template process by the ring-opening polymerization induced by radicals. The polyethylene template was connected with 2,2-diphenyl-4-methylene-l,3-dioxolane groups by the covalent bonds. The process can be illustrated by the following reaction ... 

Dioxolans. Some of the most interesting work in this series has come from Hoffmann s group in London. The debromination of aa -dibromo-ketones, e.g. (202), with a zinc-copper couple in dimethylformamide or dimethylacetamide gives 2-dimethylamino-4-methylene-l, 3-dioxolans (203). These compounds can be regarded formally as 1,3-dipolar adducts of dimethyl amides with oxyallyl (204), or as 1-amino-acetals. Their great... 

Also an unsaturated cyclic acetal (2-isopropenyl-4-methylene-l,3-dioxolane), which is formed from methacrolein and epichlorhydrine, can be polymerized via ring-opening-cationic polymerization [254]. 

Enols and Enolates.—The search for the hypothetical oxyallyl zwitterion (36) and the invocations of its intermediacy continue unabated reductive transformations of aa -dibromo-ketones, plausible precursors of the zwitterion, have been extensively studied. Reduction of such ketones with a Zn-Cu couple in DMF yields 2-dimethylamino-4-methylene-l,3-dioxolans (37), by... 

The monomers 4-methyl-l,3-dioxene-4 and 2-trichloromethyl-4-methylene-l,3-dioxolane and other 4-methylene-l,3-dioxolanes are known to also undergo spontaneous copolymerization, with MA at temperatures >50 C, giving good yields of low-molecular-weight, alternating copolymer. The equimolar 4-methyl-l,3-dioxene-4-MA copolymer structure 11 is shown below. 

Poly(methylenecyclopentene-alt-MA), 350 Poly(4-methylene-l,3-dioxolane-alt-MA), 321, 660 Poly(2-methyleneoxetane-co-MA), 320 Poly(2-methylenepropanediol-alt-MA), 311 Poly(2-methylfuran-alt-MA), 320, 322 Poly(4-methyl-l-hexene-alt-MA), optically active polymer, 317... 

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