On the reactions of (vinylimino)phosphoranes and related compounds. Part 30. Short new synthesis of 5-azaazulene derivatives. Some comments on reactivities of (vinylimino)phosphoranes

Abstract

A short new synthesis of phenyl-substituted and annulated 5-azaazulene (cyclopenta[c]azepine) derivatives 15-18 consists of the reaction of [( 1 -phenylvinyl)imino]-and benz-annulated [(cycloalkenyl)imino]phosphoranes 8-1 1 with 5-(dimethylaminomethylene)cyclopenta-l,3-dienecarbaldehyde 1 in an enamine alkylation (Michael addition) process, subsequent proton migration-ketonization, and condensation of the formyl group with the iminophosphorane moiety (aza-Wittig reaction). On the other hand, reactions of aldehyde 1 with (viny1imino)phosphoranes 12-14, which have no phenyl group at the or-position relative to the nitrogen atom, consist of a intramolecular aza-Wittig reaction or a substitution reaction of aldehyde 1 with phosphoranes 12-14 and subsequent hydrolysis to afford 5-(aminomethylene)cyclopenta-1,3dienecarbaldehyde 19 and its derivatives 20 and 21, respectively. In the context of selectivity observed in the reaction of phosphoranes 8-11 and 12-14 with aldehyde 1, respectively, MNDO calculations on compounds 1 and 12A, 12B as well as on model compounds 8C-12C were performed to gain insight via a theoretical interpretation based upon frontier molecular orbital theory (FMO): the former reaction, giving 5-azaazulene derivatives, would be an FMO-controlled reaction, while the latter is a charge-controlled reaction. Several spectral and chemical properties of heterocycles of 16-18 are analysed.

Aza-Wittig Reaction of N-Vinylic Phosphazenes with Carbonyl Compounds. Azadiene-Mediated Synthesis of Isoquinolines and 5,6-Dihydro-2H-1,3-oxazines

“…Diethyl ketomalonate also reacted with azadienes 1. However, in this case the presence of LP-Et 2 O as a catalyst was required 23 and afforded a mixture of cycloadducts 12 and 12′ (Scheme 5), with a higher proportion of cis isomer 12 than the trans isomer 12′ (Table 3, entries [7][8][9][10][11][12][13][14][15][16][17]. Formation of 1,3-oxazines 12/12′ can also be explained through a two-step cycloaddition process, although now the presence of two substituents in position 6 of compounds 12/12′ as opposed to the presence of only one substituent in heterocycles 11 could explain the formation of both isomers 12 and 12′, but with a higher proportion of the more stable 12.…”

Synthetic Applications of Intramolecular Aza-Wittig Reaction for the Preparation of Heterocyclic Compounds

“…The same group has demonstrated the versatility of the enamine-type alkylation of vinylic phosphazenes/intramolecular aza-Wittig protocol, for the preparation of other fused nitrogen heterocycles [17]. Thus, the synthetic strategy for the preparation of 11H-cyclohepta for the construction phenyl-substituted and annulated 5azaazulene (cyclopenta[c]azepine) derivatives [18].…”

N-Vinylic Phosphazenes. A Useful Tool for the Synthesis of Acyclic and Heterocyclic Compounds

“…Thus, 5H-dicyclohepta[b,d]pyrrole ring system 120 can be obtained through an enamine-type alkylation of the phosphazene 117 onto C of cyclic conjugated ketone 118 to give a keto-functionalized phosphazene 119 (Scheme 38). This methodology has been also used to construct phenyl-substituted and annulated 5-azaazulene (cyclopenta[c]azepine) derivatives [49]. Scheme The same group has demonstrated the versatility of the enamine-type alkylation of vinylic phosphazenes/intramolecular aza-Wittig protocol, for the preparation of other fused nitrogen heterocycles [48].…”