Repetitive reaction steps

RNH2 core building block — rep.1 - repetitive reaction steps... 

The 2° radical abstracts a H-atom from HBr. This leads to the product and regenerates a Br-atom. Then repetitions of steps 3 and 4 lead to a chain reaction. 

Figure 10.7 Autoxidation of a linoleic acid ester. In step 1 the reaction is initiated by the attack of a radical on one of the hydrogen atoms of the -CH2-group between the two double bonds this hydrogen abstraction produces a radical that is a resonance hybrid. In step 2 this radical reacts with oxygen in the first of two chain-propagating steps to produce an oxygen-containing radical, which in step 3 can abstract a hydrogen from another molecule of the linoleic ester (Lin-H). The result of this second chain-propagating step is the formation of a hydroperoxide and a radical (Lin ) that can bring about a repetition of step 2.

Thus, the synthesis of dendrimers consists of two constantly repeating reaction steps. The first step deals with the linkage of a branching unit to two other units - the construction step. In the second reaction, groups are transformed, so that they can react further - the activation step. This procedure is also referred to as an iterative (repetitive) strategy.131... 

The polymerization of cyclic, strained olefins by transition metal alkylidenes of general formula L M = CRR (L = ligand, R, R = H, alkyl, aryl) yields polymers formed via ring-opening that contain unsaturated double bonds within each repetitive unit. Since the mechanism is based on repetitive metathesis steps, this polymerization reaction is known as ring-opening metathesis polymerization (ROMP) (Scheme 1). 

Propagation can proceed with the repetition of steps (3-4) to (3-6) involving the aewly formed species, HA, to form a polyester. It was assumed that reaction (3-6) was rate-controlling, and that the concentrations of active species were in a stationary state, which led to a prediction of an overall second-order dependence of rate on anhydride or epoxide concentration. 

The peptide synthesis consists of stepwise-condensation and segment-condensation procedures. In both procedures, it is possible to purify the reaction product at each reaction step. Therefore, protected peptides with a high degree of purity can be obtained from a solution method. The choice of the reagents used in the final deprotection step determines the main strategy of peptide synthesis. The final deprotection procedures are mainly (1) catalytic hydrogenolysis in the presence of palladium,(2) sodium treatment in liquid ammonia for 10 to 15 seconds, repetitively over 30 minutes,(3) TFA treatment at room temperature for 1 hour,t l (4) HF treatment at 0°C for 1 hour,t l or (5) hard-soft acid-base procedure.0 ... 

Repetitive strategy is a fundamental principle for the synthesis of dendrimers, that was first coined, to the best of our knowledge in our seminal cascade paper.1 It implies a repetitious sequence of the same reaction steps, as initially demonstrated in the synthesis of linear polyamines,1 by sequential Michael addition, followed by a facile nitrile reduction (Scheme 1). The preparation of Newkome s arborols5 is an-... 

Conversion of dihydroxy compounds to diamines requires the repetition of all reaction steps (dehydrogenation, addition, elimination, hydrogenation). Selectivity is much higher when diols are transferred only to amino alcohols or amino alcohols to diamines. This difference is exemplified by the reaction of 1,6-hexanediol with di-methylamine over CU/AI2O3 [25]. Over 90% selectivity for the intermediate N,N-dimethyl-6-amino-l-hexanol was achieved at 180 °C in a continuous fixed-bed reactor. To complete the amination of the second OH group the reactor temperature had to be raised to 230 °C and the highest selectivity for diamine was only 65 %. 

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