[mevans86]

Hey all! New member here. I'm putting together some materials on organic synthesis, and I'm having writer's block when it comes to referring to "the opposite of a retron"...essentially the starting materials of a transformation. "The starting materials of the reaction" is crazy cumbersome to write out compared to "retron," but I don't know of a technical term for the starting materials. "Synthon" comes to mind, but this term is typically used to refer to fantastical fragments of molecules, rather than starting materials.

Expert advice would be appreciated! 

[discodermolide]

A retron is an intermediate in a reterosynthetic pathway. A synthon is an actual molecule which can be employed to carry out a part of a synthesis.
Synthon does not necessarily mean retron.
 

[Arkcon]

Thanks, discodermolide:, I was expecting this was a question involving biochemistry.  I'll move this back now.

[mevans86]

I hear you disco; I guess my prevailing notion of "synthon" is that a synthon is not a true molecule, but an extreme analogue showing the intrinsic reactivity of a particular species or how it might be transformed later into something else. For example, lithiated thioacetals reflect the acyl anion synthon. My question is: what do you call the lithiated thioacetal itself?

I may have just answered my own question. I think the "synthon" here is the lithiated thioacetal, and it's called the "synthetic equivalent" of the acyl anion. Can anyone confirm? This may seem like a goofy terminology question, but I'm trying to get it straight.

I realize that retrons and synthons are definitely not the same thing. 

[discodermolide]

Yes it is the synthetic equivalent of the acyl anion.
Synthons can be any molecule that can be transformed to the product. They can be big or small, but they are real molecules.
Hanessian also coined the term "Chiron" which is a chiral synthon, e.g. amino acids, carbohydrates, terpenes and the like.