“…Of course, as is the case in all Tröger's base reactions, other by-products, such as 3,4-dihydroquinazolines (the products of a condensation between two anilines and two formaldehyde equivalents) [28,[56][57][58][59][60][61] and related products (for example, condensation between three anilines and four formaldehyde equivalents), [6,62] can also be formed. Clearly, the use of two different anilines in the reaction can magnify these types of impurities, which may complicate purification of the desired hybrids.…”