Divinyl-zinc

SCHEME 7.97 Divinyl zinc additions and mercury cyclizations. 

Following the success of the elimination-allylation and propargylation sequences, Madsen and coworkers investigated the corresponding elimination-vinylation reaction [37]. The vinylation, however, cannot be carried out directly under Barbier conditions because vinyl bromide does not insert zinc under the conditions for the reductive elimination preformed divinyl zinc was used instead [51,52], Treatment of iodo furanoside 55 with zinc dust and divinyl zinc in THF gave diene 56 in a good yield (85%) and excellent diastereoseleetivity (10 1) (Scheme 3.18). 

One exception is the reaction of acetone oxime with divinyl ketone in the presence of an equimolar amount of zinc(II) bromide (162). Acetone oxime reacts with divinyl ketone on heating in THE at reflux, leading to both conjugate addition and nitrone cycloaddition, producing a 5 1 mixture of regioisomers with 8-oxa-l-azabicyclo[3.2.1]octan-4-one as the major isomer (Scheme 11.42). On the other hand, in the presence of an equimolar amount of zinc(II) bromide, 7-oxa-l-azabicyclo[3.2.1]octan-4-one is the major isomer (97 3) in a total yield of 97%, indicating that the Lewis acid has controlled the regioselectivity of the second step, namely, the cycloaddition. 

M.U. Kahveci, M.A. Tasdelen, and Y. Yagci, Photo-induced cross-linking of divinyl ethers by using diphenyliodonium salts with highly nucleophilic counter anions in the presence of zinc halides. Macromol. Rapid Commun. 2008, 29(3), 202-206. 

Zinc diethyidithiocarbamate Talc BC IMP1889L 1,4-Cyclohexanedimethanol divinyl ether Alcan FRF 20... 

Parks [17] described an absorbent polymer prepared by copolymerizing acrylic acid with a divinyl crosslinker such as tetraethyleneglycol diacrylate, at a concentration of about 10% in aqueous solution, with sodium persulfate as initiator at 60 C. The polymer was neutralized with sodium hydroxide and then mixed with a solution of divalent ion salt, such as zinc acetate dihydrate. The product was dewatered with methanol and then oven dried to a solid product. The product was said to exhibit no gel blocking when in contact with water. Gel blocking often occurs with high swelling capacity, low modulus and sticky products. Particles that are first to contact the fluid swell very rapidly and cause lumps with unswollen particles, which swell no further due to reduced water transport through the gel. 

Sometimes, ion-exchanging groups are introduced on to the resins and these are synthesized by first preparing the styrene-divinyl benzene copolymer [as in Eq. (1.7.1)] in the form of beads, and then the chloromethylation is carried out. Chloromethylation is a Friedel-Crafts reaction catalyzed by anhydrous aluminum, zinc, or stannous chloride the polymer beads must be fully swollen in dry chloromethyl methyl ether before adding the catalyst, ZnCla. Normally, the resin has very small internal surface area and the reaction depend heavily on the degree of swelling. This is a solid-liquid reaction and the formed product can be shown to be... 

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