Chloroformate reaction specificity?

Question

In synthesis, a symmetrical anhydride is necessary to create one product when you attack with a nucleophile on the carbonyl. e.g. R-C=OOC=OR. But you can only get 50% yield this way b/c you can only use half. Our teacher said that if you use a chloroformate to make something like: RC=OOC=OOR', that it would react with the carbonyl attached to R (not R'). Why won't it react with the carbonyl of the C=OOR' group? Does it have anything to do with the extra O attached?

Answer 1

The ester group is less polar.