9.10- Dimethoxy-3,4,6,7-tetrahydro-2 pyrimido isoquinolin-2,4-dione

Catalytic hydrogenation of 3,4-dihydro-2//-pyrimido[2,l-a]isoquinoline-2,4-diones (93) and 3,3-diethyl-9,10-dimethoxy-3,4,6,7-tetrahydro-2//-pyrimido[2,l-a]isoquinoline-2,4-dione (94) over Pt02 and Pd/C catalysts gave l,3,4,6,7,llb-hexahydro-2/7-pyrimido[2,l-a]isoquinoline-2,4-diones (95) [69YZ649 71JPP71/09466]. From the mother liquid of compounds 93 (R = H, R1 = Et and R = R1 = Et) 3-ethyl-2-hydroxy-6,7-dihydro-and -8,9,10,1 l-tetrahydro-4//-pyrimido[2,l-a]isoquinolin-4-ones, and 3,3-diethyl-l,3,4,llb-tetrahydro-2//-pyrimido[2,l-a]isoquinoline-2,4-dione, also could be isolated as minor products. Reduction of 3,3-diethyl-l,3,4,6,7,llfo-hexahydro-2//-pyrimido[2,l-a]isoquinoline-2,4-dione (95, R = R1 = Et, R2 = H) with LAH in tetrahydrofuran at 70°C for 9 h afforded 3,3-diethyl-l,3,4,6,7,llb-hexahydro-2//-pyrimido[2,l-a]isoquinoline (96). 

Reaction of 9,10-dimethoxy-3,4,6,7-tetrahydro-2//-pyrimido[6,l-a] isoquinoline-2,4-diones (84JMC1470) and 2-[2-(l-pyrrolidinyl)ethyl]-2,3,4,4fl,5,6-hexahydro-l//-pyrimido[l,6-a]quinolin-l-one (70USP3494922) with P4S10 gave the 2-thioxo and 1-thioxo derivatives, respectively. (In the first case the products were earlier described as 2-oxo-4-thioxo derivatives [77SAP77/06706 78GEP2720085 79GEP2801289],... 

The reactions of l-aminocarbonylmethylene-3,4-dihydro- and 1,2,3,4-tetrahydroisoquinolines with lV,lV-dimethylcarboxamide diethyl acetals, triethyl orthoformate, and diethyl carbonate yielded 6,7-dihydro-2//-pyrimido[6,l-a]isoquinolin-2-ones [81KFZ(5)44 82KGS1095 84JMC1470] and 9,10-dimethoxy-3,4,6,7-tetrahydro-2//-pyrimido[6,l-n]isoquinoline-2,4-dione (84JMC1470), respectively. A mixture of l-ethoxycarbonyl-9,10-dimethoxy-3,4,6,7-tetrahydro-27/-pyrimido[6,l-fl]isoquinoline-2,4-dione and l-[cyano(ethoxycarbonyl)methylene]-l,2,3,4-tetrahydroisoquinoline was obtained when 6,7-dimethoxy-l-aminocarbonylmethylene-l,2,3,4-tetrahydroisoquinoline was reacted with ethyl chloroformate in methylene chloride in the presence of pyridine (84JMC1470). 

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