From Spiro Heterocyclic Substrates

A few miscellaneous spiro heterocyclic compounds have been shown to act as substrates for the primary synthesis of regular quinoxalines. However, none of the following recent examples appears to have much potential as a preparative method. 

6-Phenylsulfonyl-1,3-dihydrospiro[2//-benzimidazole-2, l -cyclohexan]-5-amine (601) gave 7-phenylsulfonyl-6-quinoxalinamine (602) [MeOH-H20, 60°C, 20 min then (CH0)2-NaHS02, 95°C, 5 min 55% clearly a two-stage one-pot synthesis via the unisolated intermediate shown] 538 7-morpholino-6-quinoxalinamine was obtained (57%) by a similar reaction.538 

4 -Methyl- 3 -, 4 -dihydrospiro[pyrimidine-5(2//),2 (1 7/)-quinoxaline] -2,4,6( 1 //,3//)-trione (605) gave l-methyl-3-ureidocarbonyl-l,2-dihydroquinoxaline (606) (2M Na2C03, 15% H2O2, then AcOHj 74% two homologs similarly mechanism discussed).  

4-Dihydro-2//-pyrimido[2,l-a]phthalazine-7(6//)-one (331) suffered acylative ring fission to give 2-(3-acetamidopropyl)-3-acetyl-1,4(2//,3f0-phthalazine-dione (332) (AC2O, reflux for further details, see original).  

This type of synthesis is very poorly represented in the more recent literature by the following examples. 

8 -Dihydro spiro [cyclohexane-1, l -[ l//]-diazirino[l, 2-/ ]phthalazine] -3, 8 -dione (333) underwent acidic hydrolysis with loss of cyclohexanone to afford l,4(2//,3//)-phthalazinedione (334) HCl, MeOH, reflux, 90 min %) or thermolytic isomerization to afford 2-(cyclohex-l-enyl)-l,4(2//,3//)-phthala-zinedione (335) (PhMe, reflux, 2 h 70%).  

In contrast, 2-hyd oxy-3, 8 -dihyd o spi o[cyclohexane-l,l -[l /]-diazi ino[l,2-f ]phthalazine] -3, 8 -dione (336) underwent thermal or base-catalyzed isomerization to furnish 4-(2-oxocyclohexyloxy)-l(2//)-phthalazinone (337) (PhMe, reflux, 2h 55% or Bu OK, Me2SO, 20°C, 12 h 85% ) a rational mechanism was proposed. 

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