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We have observed that when 2-thiomorpholino-5-trifluoromethylbenzaldehyde is reacted with barbituric acids under Knoevenagel condensation conditions, a novel heterocyclic system is formed: 1,2,4,4a,5,6-hexahydrospiro [[1,4]thiazino[4,3-a]quinoline-5,5'-pyrimidine]-2',4',6'-triones 1a,b, i.e., two new C-C bonds are formed during the reaction. The reaction occurs through the o-vinyl derivatives 3 [1, 2] followed by their cyclization according to a tert-amino effect mechanism [3,4]. When monosubstituted barbituric acids were used, two isomers could be formed. We have shown that with monosubstituted barbituric acid 2b, a 1:1 mixture of spiro-linked condensed [1,2-a]quinolines 1b is formed in 78% yield. One of the isomers can be isolated in 33% yield by fractional crystallization from aqueous alcohol.

The reactions of 2 (3,5 dimethylpiperidino)benzaldehyde with Meldrum´s acid and cyclo hexane 1,3 dione occur as a tandem of the Knoevenagel condensation and cyclization pro moted by the tert amino effect. The cyclization yields only one isomer with the axial hydrogen atoms in positions 4 and 4a of the benzoquinolizine ring.

The term "tert-amino effect" was proposed by Meth-Cohn and Suschitzky [1] for the general reaction of cyclization of some derivatives of ortho-substituted N,N-dialkylanilines. The cyclization which occurs at the unsaturated α-carbon atom of the dialkylamino group, was described for compounds with an unsaturated (A=B) ortho substituent, including at least one heteroatom (nitroso-, azo-, azomethino-, nitro-, amino-, or carbonyl functions) [2]. Professor Reinhoudt's group established that cyclization also took place with N,N-dialkylanilines with a vinyl substituent in the ortho position [3]. This reaction is an original method for the formation of a C-C bond with an unactivated NCH 2 group [4].We have shown previously [5][6][7][8] that the Knoevenagel condensation occurs in tandem with cyclization via the tert-amino effect mechanism when 2-dialkylaminobenzaldehydes react with cyclic CH-active compounds (derivatives of 1,3-cyclohexandione, Meldrum's acid, barbituric acid) [9]. These reactions were shown to occur stereoselectively [4, 10-12].The aim of the current work was to investigate the reaction of 2-piperidinobenzaldehydes 1a-d with 2-aryl-5-methyl-2,4-dihydropyrazol-3-ones 2a-c. The reactions were carried out in boiling butanol. 3'-Methyl-1 '-phenyl-2,3,4,4a,5,6-hexahydro-6H-spiro[benzo[c]quinolizine-5,4'-pyrazol]-5'-ones 3a-j (Table 1) were formed as a result. The reaction products contain two asymmetric centers, so it is consequently possible to form two diastereoisomers. It was shown that the reaction proceeded stereoselectively and led predominantly to a single diastereomer (up to 95-98%).In the 1 H NMR spectrum of the basic reaction product ( Table 2) the signal of the proton on the carbon atom 4a appears as a doublet of doublets in the 3.13-3.18 ppm region. This proton interacts with a large coupling constant of 11.2-11.5 Hz with the axial hydrogen in position 4 and with a small coupling constant of 2.3-2.5 Hz with the equatorial hydrogen in the same position. Hence the hydrogen in position 4a occupies an axial position.

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