Synthesis of DHPMs and Thiazines

DHPMs are interesting heterocycles as they are present in some pharmacologically active natural products as 

SCHEME 6.41 Synthesis of highly functionalized novel dispiropyrrolidines 267-271. 

SCHEME 6.42 Synthesis of polycyclic alkaloids using an Ugi/Michael/aza-Michael cascade reaction. 

It is thought that the orientation of the substituent acts as a molecular switch between agonist and antagonist activities [86]. Thiazines are the 2-thio analogues of DHPM and are used for dyes (methylene blue), tranquilizers, and insecticides. 

Classically, they are built through a Biginelli reaction between urea, aldehydes, and p-ketoesters in protic solvents under strongly acidic conditions [87]. The yield of this original reaction is rather low and side reactions occur very often [88], In this sense, great effort has been devoted in the last years, focused on the research of this MCR (see Chapter 9). However, the discovery of new reactions for the preparation of this kind of compounds is 

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