Models for incomplete nucleophilic attack on a protonated carbonyl group and electron-deficient alkenes: salts and zwitterions from 1-dimethylamino-naphthalene-8-carbaldehyde

Abstract

The X-ray crystal structures of salts and zwitterionic Knoevenagel products from 1-dimethylaminonaphthalene-8-carbaldehyde show long N-C bonds between peri-groups which provide models for incomplete nucleophilic attack on a protonated carbonyl group and electron-deficient alkenes respectively. For the salts the N-C bonds lie in the range 1.625-1.638 Å with C-OH bonds intermediate in length between single and double bonds, while for the zwitterions the N-C bonds lie in the range 1.612-1.660 Å. The structural assignment of the former is supported by solid state 13 C and 15 N NMR studies on doubly isotopically-labelled material. Several zwitterions were converted to naphtha[1,8-bc]-azepines by a mechanism involving the tertiary amino effect.

O-vs. N-protonation of 1-dimethylaminonaphthalene-8-ketones: formation of aperiN–C bond or a hydrogen bond to the pi-electron density of a carbonyl group

“…Bond formation is a fundamental process in chemistry, and its study underpins topics such as catalysis and enzyme action. The peri-naphthalene system has provided us with a series of zwitterionic materials such as 1-3 with N-C bonds in the range 1.612(2)-1.6536 (14) Å, [1][2][3] significantly longer than a typical unperturbed N-C bond of ca. 1.47 Å.…”

Modelling of an aza-Michael reaction from crystalline naphthalene derivatives containing peri–peri interactions: very long N–C bonds?

“…Furthermore, the difference of 16-17°i n the exo angles at the fusion the benzene rings between the two peri positions (ϕ and ψ in Table 1) shows how the widening of the ϕ angle between the amino and alkene groups has been caused by the compression of the ψ angle which was imposed by the short ethylene bridge: i.e. ϕ: 127.30 (18)/128.54 (17)°vs. ψ: 111.73 (17)/111.…”

“…The expected unit cell dimensions were confirmed by powder X-ray diffraction The "open" analogue 3 (Me 2 N⋯C: 2.413 Å) and the "closed" analogues 4 and 22-23 (Me 2 N⋯C: 1.612(2)-1.651(3) Å) provide references for the chemical shift of this labelled carbon atom at its possible extreme positions: 165.6 and 88.9-99.1 ppm respectively. 16,17 In solution both the salt 13•Cl and free base 12 show that they are in the "open" structure with the alkene carbon atoms at 163.1 and 73.4 ppm for 13•Cl and 165.8 and 73.0 ppm for 12 in CD 2 Cl 2 .…”

“…23 Among the peri-naphthalenes the longest N-C bonds between peri-substituents are in cations 17 and 18 and zwitterion 19 and are in the range 1.66-1.68 Å. 15,17,24 4and 1.749(3) Å respectively. A bond between the functional groups is drawn in the latter case, to indicate the closer distance.…”

“…16 In the first of these the nucleophile impinges on an alkene terminated by two nitriles with a Me 2 N⋯C separation of 2.413(2) Å while in the latter case, where the alkene is activated by two in-plane lactone carbonyls, the groups reacts to form a zwitterion with a long Me 2 N-C bond of 1.651(3) Å. Although a range of such systems has been studied, 17 no such structures with Me 2 N⋯C separations in the range 1.7-2.4 Å have been found. Indeed, the only molecular structure with such N⋯C separations are for transannular interactions across the ring systems of particular alkaloids, such as clivorine 5 (1.93 Å) and senkirkine 6 (2.25 Å), 18 as highlighted by Bürgi, Dunitz and Schefter.…”