Pyrazines from Spiro Heterocycles

The only spiro systems used as substrates for preparing pyrazines appear to be those involved in the following examples  

4-Benzyl-l-oxa-4-azaspiro[4.5]decane (149, R = CH2Ph) gave 1,4-diben-zylpiperazine (150, R = CH2Ph) and cyclohexanone (polyphosphoric acid, 200°C, 10 h 40%) 413 l,4-bis(2-hydroxyethyl)- (150, R = CH2CH2OH) and 1,4-diphenylpiperazine (150, R = Ph) were made similarly and in comparable yields.413 

6-Benzylidene-4,7-dimethyl-2-phenyl-l-oxa-4,7-diazaspiro[2.5]octane-5,8-dione (151) gave 3-bcnzoyl-6-bcnzylidcne-l,4-dime(hyl-3,6-dihydro-2,5(177, 477)-pyrazinedione (152) (TsOH, PhMe, reflux, water removal ( ), 18 h 73%).1030 

APPENDIX GLANCE INDEX TO TYPICAL PYRAZINE DERIVATIVES AVAILABLE EROM OTHER HETEROCYCLIC SYSTEMS 

This glance index is provided to assist in the choice of a primary synthesis that may provide a required type of pyrazine derivative from another heterocyclic system. Procedures that afford very poor yields or employ substrates that are difficult of access are omitted so too are those methods that appear to lack general applicability in their present state of development. However, such syntheses are often of great interest and may prove invaluable in the right context. 

---