Stereochemical Aspects of the “tert-Amino Effect” : 1. Regioselectivity in the Synthesis of Pyrrolo[l,2-a]quinolines and Benzo[c]quinolizines

摘要: Substituted 2-vinyl-N,N-dialkylanilines cyclize in refluxing 1-butanol to give substituted pyrrolo[1,2-α] quinolines and benzo[c]quinolizines. This reaction proceeds via a 1,5-hydrogen transfer subsequent C-C bond formation. When the 4, R1= H R2 = (4a,d), CH3(4b,e), or C2H5(4f), cyclization products 5a,b,d-f are formed selectively, with substituent R2at bridgehead carbon atom. regioselectivity is lost when CH2OCH3(4c,g), mixture of regioisomers 5c,g, 6c,g, 7c,g formed. Reaction compounds 4h-n (R1= CH3) yields pyrrolo[l,2-α]quinolines 5-7(h-j) benzo[c]quinolizines 5-7(k-n) which at atom same face molecule (cis) as hydrogen C-5 [5-7(h-j)] C-6 [5-7(k-n)]. The configuration these was determined by1H NOE difference spectroscopy single-crystal X-ray analysis (6n). Heating 4o-q 4-C6H4CH3) gives mixtures cis [5-7(o-q)] trans [8—10(o—q)] compounds. mechanism cyclizations, further examples “tert-amino effect”, effect variation substituents discussed.