Transition metal-diene complexes in organic synthesis. Part 7. Regioselectivity control in iron-mediated diastereoselective spiroannelations of arylamines: cyclization of 1-aza- versus 3-aza-spiro[5.5]undecanes.
In: Tetrahedron letters (Tetrahedron Lett.), Jg. 32 (1991) ; Nr. 17, S. 1953-1956
Zeitschriftenaufsatz / Fach: Chemie
The regioselectivity of the spiroannelation of arylamines, e.g., 2,3,4-RR1R2C6H2NH2 [I, R = R1 = H, Me; R1 = MeO; RR1 = (CH:CH)2, R2 = MeO], with tricarbonyliron-complexed h5-cyclohexadienylium cation II is governed by the substituents of the arylamine. Thus, I (R = R1 = H; R2 = MeO) reacted with II to give the azaspiro[5.5]undecane complex III as the only product. However, II reacted with I [RR1 = (CH:CH)2, R2 = MeO) to give a mixt. of regioisomeric spiro cycloadduct complexes IV and V in the ratio of 1:9 resp. The crystal and mol. structure of V was detd. by x-ray crystallog.