REDUCTIVE ALKYLATION OF PYRIDINIUM SALTS .2. UTILIZATION OF DI-HYDROPYRIDINE, TETRA-HYDROPYRIDINE AND HEXA-HYDROPYRIDINE ESTERS

4-Benzyl-4-ethoxycarbonyl-1-substituted piperidines 1 (R(1) = PhCH(2), PhCO; R(2) = PhCH(2)) cyclise with polyphosphoric acid (PPA) to give spiro [indane-2,4'-piperidin]-1-ones 3 (R = PhCH,, PhCO), while 2-benz yl-2-ethoxycarbonyl-1-methylpiperidine 4 gives the N-methylspiro [inda ne-2,2'-piperidin]-1-one 5. 3,4,4a, 5-Tetrahydrobenz[g]isoquinolin-10( 2H)-one 8 arises from PPA treatment of benzyl-5-ethoxycarbonyl-1,2,3,4 -tetrahydropyridine 7 (R = PhCO) while o-chloranil converts 1-benzoyl- 4-benzyl-4-ethoxycarbonyl 1,4-dihydropyridine 6 (R = PhCO) into 4-benz yl-3-ethoxycarbonylpyridine 9. Phenyl(tribromomethyl)mercury reacts wi th zoyl-4-benzyl-4-ethoxycarbonyl-1,4-dihydropyridine 2 (R(1) = PhCO, R(2) = PhCH(2)) yielding l-7,7-dibromo-5-ethoxycarbonyl-2-azabicyclo[4 .1.0] hept-3-ene 11, and with zoyl-4-benzyl-3-ethoxycarbonyl-1,4-dihyd ropyridine 6 (R = PhCO) to give omo-4-ethoxycarbonyl-2-azabicyclo[4.1. 0]hept-3-ene 12, The structure of the latter is confirmed by X-ray cry stallographic analysis. Catalytic hydrogenation of 2-benzoyl-5-benzyl- 7,7-dichloro-5-ethoxyca [4,1,0]hept-3-ene 16 yields -benzyl-7,7-dichlo ro-4-ethoxycarbonyl-2-azabicyclo [4,1,0]heptane 21 which cyclises with PPA to give the tetracyclic product 22 in good yield, When 2-benzoy-5 -benzyl-7,7-dichloro-4-ethoxycarbonyl azabicyclo[4.1.0] hept-3-ene 17 is hydrogenated it yields mainly nzyl-7,7-dichloro-4-ethoxycarbonyl-2- azabicyclo[4. 1.0]heptane 25 but the dibromo analogue 12 under the sam e conditions gives two components thought to be -benzoyl-5-benzyl-7-en do-bromo-4-ethoxycarbonyl-2- azabicyclo [4.1.0]hept-3-ene 24 and l-7-e xo-bromo-4-ethoxycarbonyl-2-azabicyclo[4,1,0] hept-3-ene 23.