Silver, assisted cleavage

Release by Silver-Assisted Cleavag e. A soluble silver complex formed imagewise in the undeveloped areas of the silver haUde layer may be used to effect a cleavage reaction that releases a dye or a dye precursor. The process yields positive dye transfer images directiy with negative-working emulsions (46). An example is the silver-assisted cleavage of a dye-substituted thiazolidine compound, as shown in equation 7. 

Fig. 14. Schematic cross section of Spectra integral film. The 600 Plus film has a similar stmcture. In these films the yellow image is formed by silver-assisted cleavage of a yellow dye releaser. A colorless developer reduces exposed silver hahde in the blue-sensitive emulsion in unexposed areas dissolved silver diffuses to the dye releaser layer and triggers the release of the yellow image dye.

Discrimination between exposed and unexposed areas in this process requires the selection of thia zolidine compounds that do not readily undergo alkaline hydrolysis in the absence of silver ions. In a study of model compounds, the rates of hydrolysis of model /V-methyl thia zolidine and A/-octadecyl thiazolidine compounds were compared (47). An alkaline hydrolysis half-life of 33 min was reported for the /V-methyl compound, a half-life of 5525 min (3.8 days) was reported for the corresponding V/-octadecyl compound. Other factors affecting the kinetics include the particular silver ligand chosen and its concentration (48). Polaroid Spectra film introduced silver-assisted thiazolidine cleavage to produce the yellow dye image (49), a system subsequentiy used in 600 Plus and Polacolor Pro 100 films. 

In general, virtually any process leading to 4-azetidinylthioesters from penams was put to its best use by the oxoamide-thioester coupling. Preparation of FCE-22101, FCE 22891 and related penems, could be achieved in fewer steps [81,82,92,96,153]. In particular, the silver-assisted 1,2-cleavage of penicillins is ideally suited to accompany the phosphite-mediated condensation a unique... 

The silver-ion-assisted cleavage of (187 X = Cl or Br) has been re-examined and the previously undetected (189 X = Cl or Br) isolated. The presence of this product is taken as evidence for ring-opening of the cyclopropyl cation (188) as the method... 

The silver ion assisted carbon-halogen bond cleavage and the unraveling of the cyclopropane ring by the cyclopropyl-allyl rearrangement was first noted in the formation of 2-bromocyclohexen-l-ol from dibromobicyclo[3.l.0]hexane under solvolytic conditions (equation 86).220 The silver ion assisted solvolysis of the dihalocyclopropane adduct (43), derived from a Birch reduction product, smoothly rearranges to the tropone (equation 87).221 A number of other synthetic applications222-226 have beien reported... 

In certain cases, the silver ion assisted solvolysis fails to initiate electrocyclic reaction to give ring-expanded compounds, leading instead to a cleavage product (equation 90).227 The dichlorocarbene adduct (48) on FeCb-promoted cleavage in ether affords exclusively a-trichloromethylcyclohexanone, whereas in DMF a small amount of chlorocycloheptenone also was obtained (equation 91).228... 

The hitherto unknown tropylium ion isomer (317) has been generated from both (315) and (316). ° In carbon tetrachloride at 80°C, (315) affords (31 probably by disrotatory ring cleavage and loss of the endo-bromine atom. Although (317) is stable, silver-ion-assisted solvolysis of (316) causes partial rearrangement of (317) into the norbornene manifold (Scheme 40). 

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