Problem+12

Before reading the full discussion of this problem in the PDF file below, there are a few leads:

1.- As yourself which is apparently easier to explain, either **3** or **4**, and start by the easiest one

2.- In **3** the methytl sulfide group is exported whereas it is preserved in **4**. What type of reaction you know is capable of expeling the SMe group or any other good leaving group, in a highly unsaturated compound such as **1**?

3.- Is the fused 'twin' pyranoketone rings the result of some sort of dimer of **1**, or does **2** participate in this?

4.- Regarding **4**, pay particular attention to the high oxidation level of **1** and **2** relative to the lower oxidation level of 4, and how to manage this change without reducing agents in the medium.

Further hints and reasoing details are expanded in the discussion (PDF file for free download)