Difunctional reagents

Heterocyde syntheses are often possible from difunctional open-chain precursors, including olefins as 1,2-difunctional reagents, and an appropiate nucleophile or electrophile containing one or more hetero atoms. The choice of the open-chain precursor is usually dictated by the longest carbon chain within the heterocyde to be synthesized. 

Difunctional reagents, for example the very cheap dimethyldichlorosilane 48, which is produced on a large technical scale, and the much more reactive and expensive dimethylsilyl bis(O-triflate) 49 [65-67] (Scheme 2.8) convert alcohols or phenols 11 in the presence of bases, for example triethylamine or DBU, into the silylated compounds 50. Thus 48 and 49 and other bifunctional reagents such as di-tert-butyldichlorosilane [68] or di(tert-butylsilyl)-bis(0-triflate) [69] and the subsequently described 51 and 52 combine two alcohols to silicon-tethered molecules 50, which can undergo interesting intramolecular reactions [70-74]. 

The reactions of chlorocyclophosphazenes with difunctional reagents such as diamines, diols, or amino alcohols can in principle lead to the formation of several products. These are shown in Fig. 19. The reactions of these reagents with the chlorocyclophosphazenes are discussed below. 

The reactions of the six-membered chlorocyclophosphazene were studied with a number of aliphatic diamines (169 175), aromatic diamines (176), aliphatic diols (177-179), aromatic diols (180,181) and compounds containing amino and hydroxyl functional groups (169,170,182). This subject has been reviewed (11,16,20). There are at least five different reaction products that are possible (Fig. 19). Replacement of two chlorine atoms from the same phosphorus atom produces a spirocyclic product. Replacement of two chlorine atoms from two different phosphorus atoms in the same molecule produces an ansa product. Reaction of only one end of the difunctional reagent, resulting in the substitution of only one chlorine atom, leads to an open-chain compound. Intermolecular bridged compounds are formed when the difunc-... 

Fig. 19. The possible products in the reaction of difunctional reagent with N3P3C1,...

Most aromatic difunctional reagents react with N3P3Cl6 to afford spirocyclic products (20,176,180,181,189,190). With catechol, the trispiro product is observed (190). This product was shown to function as a host in the formation of several inclusion adducts, including polymers (191). Ring degradation of the cyclophosphazene ring occurs in the reaction with o-amino phenol as well as in the reaction with catechol in the presence of a triethylamine (192). 

Phospha(thia)zenes with four coordinate sulfur atoms continue to exhibit interesting chemical and biological properties. The reactions of NPC12(NSOX)2 (X=Ph,Cl,F) with the aliphatic difunctional reagents NH2(CH2)2 3YH (y=NH, O) give the spirocyclic derivatives NP[NH(CH2)2 3Y] (NSOX) 2. The " P nmr chemical shifts of... 

The other general route to [l,2,4]triazolo[4,3- ]pyrimidine derivatives is the reaction of 3-amino[l,2,4]triazole with 1,3-difunctional reagents. Five such approaches are summarized in Table 24. As Table 24 reveals, the yields are high in all cases. 

These structures are well defined by conducting the polymerization in the presence of appropriate mono- and difunctional reagents. They are of considerable interest for the preparation of segmented block copolymers.24,25 For instance, the fluorinated macrodiols 21 have already been used to prepare an interesting new series of partially fluorinated segmented polyurethanes,26 and we are investigating other novel polymers that can be prepared from these intermediates. 

Spirocyclic product is formed as a result of replacement of both the chlorines on the same phosphorus atom, while the ansa product is formed as a result of the replacement of chlorines from two distinct phosphorus atoms within the same molecule. In open chain product only one end of the difunctional reagent is involved in reaction with the chlorocyclophosphazene. Finally, intermolecular bridged products result from the reaction of two chlorocyclophosphazene molecules with a difunctional reagent. This last reaction also is a model reaction for condensation polymerization involving phosphazenes. 

In contrast to NjPjCle, N4P4Q8 is extremely reactive towards difunctional reagents. This has led to the isolation of several decomposition products. Reactions with Af-methyl ethanolamine [87], 1,3-propane diol and 1,3-diamino propane afford mainly spiro products [138]. A detailed investigation on the reactions of N4P4CI8 with HO- CH2) -OH (n = 3, 4) has revealed that... 

Materials. Difunctional Reagents Isocyanatoethyl methacrylate (IEM) was supplied by Dow Chemical Co. as an experimental reagent. Meta TMI is available from Cyan amid, Inc. 

Enamines of cyclic ketones may also be used to prepare polyamides in a different type of condensation reaction (67MI11100). This polymerization involves reaction with diisocyanates (Scheme 46), with the enamine functioning as a difunctional reagent. Morpholino- and piperidino-enamines are the most effective monomers. 

Two different polymers can also be linked together using difunctional reagents which react with the end groups of both polymers... 

Now let us consider what happens if two such molecular threads containing didentate metal-binding domains are twisted into a helical arrangement after co-ordination to a tetrahedral metal centre. Reaction with the difunctional reagent could proceed in several ways. For example, the result could be the formation of a [2+2] macrocyclic complex as a result of the difunctional reagent linking together the two molecular threads (Fig. 7-38). 

Figure 7-38. The formation of a co-ordinated [2+2] macrocyclic ligand in the reaction of a helical complex with a difunctional reagent. The difunctional reagent links together the two molecular threads. The black circles represent the sites at which the molecular thread has reacted with the difunctional reagent.

Figure 7-39. We have selected our molecular threads and our difunctional reagents such that it is only possible to form [1+1] cyclic structures. The consequence is the formation of a catenane, in which the two new cyclic molecules are interlinked. Removal of the metal ion would give the free catenane, but it is not possible to separate the two rings without the breaking of a bond.

Table 10.1. Theoretical product ratios of the reaction of a difunctional reagent A with a monofunctional reagent B (A+ B—>A + AB + AB2).

As mentioned above, the statistically predicted amount of monofunctionalized product can only be obtained if both reactants are thoroughly mixed. If the difunctional reagent is poorly soluble under the reaction conditions chosen, its concentration might be lower than that of the monofunctional reagent. This can lead to large... 

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