Fused Tetracyclic Heterocycles by Thermally Initiated Intramolecular Criss‐Cross Cycloaddition of 3‐Substituted Homoallenylaldazines

Abstract

The thermally initiated intramolecular criss-cross cycloaddition of 3-substituted homoallenylaldazines 5 has been explored. Their cyclization led to interesting new fused heterocyclic systems 6 consisting of four five-membered rings with two nitrogen heteroatoms. The azines were prepared by the reaction of homoallenyl aldehydes 4 with hydrazine. The homoallenyl aldehydes 4 were synthesized by the Claisen rearrangement of new N,N-disubstituted 4-[(2-methylprop-

Intra–Intermolecular Criss‐cross Cycloaddition of Nonsymmetrical Allenylazines with Fluorinated Enones as an Initial Step in the Synthesis of4H‐Pyrrolo[1,2‐b]pyrazoles

“…[3,7,8] The second group may be considered as an intramolecular cycloaddition. Depending upon the regioselectivity of the reaction, we can observe formation of laterally [9,10] or centrally [11,12] fused heterocyclic compounds. The third group is a combination of the first and the second approaches: a combined intra-intermolecular cycloaddition.…”

Synthesizing Allenes Today (1982-2006)

“…More recently, Potáček and co-workers 41 H , 4 h , r e f l u x , 7 0 % R = R 1 = M e , 1 5 m i n , r e f l u x , 7 6 %…”

Non-symmetrical allenyl azines and their transformations leading to new heterocyclic skeletons

“…2 The synthesis of the non-symmetrical allenyl azines 5 from the allenyl aldehyde 1 can be performed by two different pathways (A and B) as shown at the following Scheme 2. In most of the cases the preparation was carried out via aliphatic or alicyclic protected hydrazone 3 from protected hydrazidate 2 and by reaction with homoallenyl aldehyde 1.…”

“…We have investigated mostly derivatives of homoallenyl aldehyde 1, because we have developed its improved preparation procedure (Scheme 1). 2 Among all the derivatives symmetrical azines play important role as educts of intramolecular criss-cross cycloadditions. 3 Fused tetracyclic compounds, formed in this fashion, as products of two successive 1,3-dipolar cycloadditions, 4 have been the source of interesting information about the mechanism of their formation and possible further transformations.…”