I remember seeing something like this a few years back - it was in a beta form. However, I think it was very expensive and also very limited (at that time) - It'd be a pretty full on piece of software that could take some random reagents to a product, and would presumably require lots a number crunching power and a great deal of time and expense for development...
I think you really are better sticking to sites like, the org chem portal and ecompounds ( and this site of course
)
get a copy of sykes too. and clayden!