Pyrazino quinoxalines, from

The only publication on the angularly condensed benzologues, pyrimido[2,l-tf]quinoxalines, describes the synthesis of 161 by formation of both the pyrimido and the pyrazino ring from [6+0] atom fragments. Compound 160, the targeted cyclocondensation product of the propanediamine derivative 159, spontaneously cyclized to the pyri-mido[2,l- ]quinoxaline A-oxide 161 (Equation 17) <2002S2687>. 

Formation of ring C of the 2,3,4,4 ,5,6-hexahydro-l-oxo-l//-pyrazino[l,2-tf]quinoxalines 255 from [6+0] atom fragments, by bond formation 7 to the ring junction nitrogen starting from the appropriately substituted quinoxalines 254 is described in a Japanese patent (Scheme 47) <1999WO99/33804>. 

The l,2,3,4,4 ,5-hcxahydro-pyrazino[2,l-t ][l,4]benzoxazinc 350 was prepared from the appropriately substituted benzoxazine 349, as shown in Scheme 56 <1997BML763, 2003JME2877>. Diethyl oxalate <2001USP6169086> and dibromoethane <2002W02002/020533> were also utilized to build the pyrazino ring of [l,4]oxazino[4,3-tf]quinoxalines. 

Isomerization of benzo[/]-l,5-diazabicyclo[3,2,2]nonene in 8.8 N HBr at 140°C yielded l,2,3,5,6,7-hexahydropyrido[l,2,3-de]quinoxaline (83 KGS677). Photolysis of dimethyl l-(quinolin-8-yl)-l,2,3-triazole-4,5-di-carboxylates in MeCN resulted in stable an/tydro-2,3-dimethoxycarbonyl-3//-pyrido[l,2,3-de]quinoxalin-4-ium hydroxides [87JCS(P1)403]. 6-Hy-droxymethyl-2-methyl-7-methoxy-l,2,3,4-tetrahydro-6//-pyrazino-[1,2-h]isoquinolin-4-one (138) was prepared from 5- [A-methyl-Ar-(ethoxy-... 

Another report describes the synthesis of pyrazino[2,3-6]quinoxaline 1,4-dioxides (123) by condensation of furoxano[3,4-Z>]quinoxaline (121) with alkynes and alkenes. The pyrazino[2,3-A]quin-oxaline 1,4-dioxides (123) are also isolated as the final products from the reaction with alkenes and oxidation of the initially formed dihydro derivatives (122) (Scheme 21) <88JHC813>. 

The same type of synthesis affords pyrazino[2,3-e]-1,2,4-triazines (329) and (330) from the diamino precursor (328), by reaction of the latter with glyoxal or phenylglyoxal, respectively. Product (329) is a dihydrate. The fully aromatic intermediate could not be isolated. Formation of (330) involves not only covalent solvation, but also an unusual TV-methylation of the presumed first-formed intermediate, and the suggested mechanism is outlined in Scheme 24 <86JHC33,93H(36)2577>. Reversing the order of polarities of the components allows [4 + 2] cyclization of pyrimidine (331) with orr/io-phenylenediamine (332), giving the benzo fused pyrazino[2,3-c][l,2,6]thiadiazine (333) (a [l,2,6]thiadiazino[3,4-6]quinoxaline]) (Equation (52)) <72ZN(B)1471>. 

Disubstituted and unsubstituted l,2,5-thiadiazolo[3,4- ]quinoxaline-4,9-diones (110) have been prepared in good yield by condensation of 5,6-diaminobenzo[c][l,2,5]thiadiazole with a-dicarbonyl reagents (Equation (62)) <92H(33)337>. These quinones were then converted into 1,2,5-thiadiazolo-, pyrazino-fused TCNQ analogues by condensation with malononitrile in the presence of TiCl4 in dry pyridine. The x-ray crystal structure determination of the product derived from compound (110 R1 = R2 = H) has been accomplished. 

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