Cis reactions with

Numbers in parentheses are the percentage of configuration retention. 6 cis, Reaction with cis-CHF=CHF. 

Reductive silylation of a-halo ketones is synthetically useful if the halo ketone can be obtained regio-chemically pure to begin with. An example is the zinc/TMS-CI reaction with (33). ... 

Apparatus and procedure Closely similar to the preparation of tert.-Ci,H3MgCl, cyclohexyl-MgCl and cyclopentyl-MgCl (see Exp. 2). The yield (estimated from the results obtained from reactions with this reagent) is at least 90%. Here, too, it is essential to use M-butyl chloride which is free from butyl alcohol. 

Both cis- and irans- 1,2-dibromoethylenes react with metal acetylides, but with different reactivity. For the competitive reaction of cis- and trans- fl-dibromoethylenes with the zinc acetylide 314 shows that the irans isomer is more reactive than the cis isomer[228,229]. It was also found by a competitive reaction with the zinc acetylide 317 that the irans vinyl monobromide 315 is more reactive than the cis isomer 316[230]. 

At Smith Kline French a general approach to cephalosporin and penicillin nuclear analogs was developed that utilizes a monocyclic /3-lactam (59) with the correct cis stereochemistry as a key intermediate. This is prepared by reaction of the mixed anhydride of azidoacetic acid and trifluoroacetic acid with imine (58) followed by oxidative removal of the dimethoxybenzyl group. This product could be further elaborated to intermediate (60) which, on reaction with a -bromoketones, provides isocephalosporins (61). These nuclear analogs displayed antibacterial properties similar to cephalosporins (b-79MI51000). 

Steroidal cis vicinal diols at the 1,2-, ° 2,3-, ° 5,6- or 11,12- " positions can be selectively protected as acetonides, prepared by reaction with acetone at room temperature or at higher temperatures in the presence of hydrochloric, perchloric or -toluenesulfonic acids. Cis nonvicinal-diols can be similarly protected. 

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