Diphenylmethyl groups

An 5-4-methoxybenzyl thioether is stable to HBr/AcOH and 12/MeOH. The latter reagent cleaves 5-trityl and -diphenylmethyl groups. 

Since hydrogenolysis resulted in only a 20% yield of the free aldehyde, a two-step procedure was developed in which the diphenylmethyl group was first cleaved with HF/anisole and then the unsubstituted semicarbazone was cleaved with formalin in 40-60% overall yield. 

By reversibly blocking position 3 with a diphenylmethyl group (72, 73), Prystas and Sorm also prepared 6-azauridine. The diphenylmethyl group was removed after ribosidization (74) by selective hydrogenolysis. The crystalline 6-azauridine obtained was identical with 6-azauridine prepared enzymatically. ... 

The preparation of vicinal diallyldiamines is illustrated by the following sequence condensation of glyoxal with benzhydrylamine yields the diimine 189, which is converted into 190 by the action of allylmagnesium chloride. The diphenylmethyl groups are then removed reductively by treatment with triethylsilane196. 

A similar approach was used in grafting Cjq onto a pregenerated lithiated polyethylene surface [121]. A polyethylene film with terminal diphenylmethyl groups was deprotonated with BuLi to yield an anionic polyethylene surface that was treated with Cg0 and quenched with methanol. The incorporation at the polyethylene surface was determined by XPS, UV/Vis and fluorescence spectroscopy. This reaction also works for polyisopropene, polybutadiene [69], poly(vinylbenzyl chloride) or poly(N-vinylcarbazole) PVK [54] with BuLi or NaH as a base. Charge-transfer interactions in the soluble fullerene-PVK derivative between the positively charged carbazole and Cjq lead to an enhanced photoconductivity compared with PVK [54]. 

The first generation (G = 1) of the dendrimer series 5 was obtained without any difficulty using the described synthetic approach above. This open-shell compound exists in two interconvertible pairs of enantiomers differing in the helicity of the three propeller-like conformations adopted by each diphenylmethyl group. 

In three-component allyltin-mediated processes, if the alkenes contain a chiral auxiliary, the allylation step proceeds with a high degree of stereocontrol [35]. In an example in Scheme 6.20, an acrylated oxazolidinone having a chiral substituent in the ring is employed as the alkene portion. Magnesium bromide is used as a Lewis acid to fix the acrylate moiety [36]. Allylation takes place diastereoselectively so as to avoid the face in which the bulky diphenylmethyl group is located. 

Acid cleavage of the diphenylmethyl group could be achieved under a variety of conditions e.g. i) 49% HBr, 100°, 45 min., ii) TFA/Anisole, reflux, 30 min. and the free aminophosphonous acid 8 then obtained by treatment of the hydrobromide salt with propylene oxide in ethanol, or simply by heating the trifluoro-acetates in ethanol. 

The poly(methyl methacrylate)s prepared in this experiment, as well as polymers formed in model reactions with silanes that contain bulky substituents (such as phenyldimethyl and diphenylmethyl groups), have predominantly syndiotactic structures identical to polymers prepared by the conventional group-transfer process. This result supports a two-step dissociative mechanism for a group-transfer process, because steric hindrance from bulky silyl groups should increase the proportion of isotactic triads in the hypothetical associative concerted propagation step. 

A diphenylmethyl group In tiUo unefUl for S-protection it is Ntahic to metal muIIn but can be removed by the other methodfi HBr-AcOH or C FuC O H. Thun a... 

A model consistent with the products obtained is shown in structure 20. The radical attacks the alkene from the face opposite the bulky diphenylmethyl oxazolidinone substituent. The bulk of the diphenylmethyl group is critically important in determining the selectivities obtained. Replacement of this bulky substituent on the auxiliary by a smaller benzyl group leads to a substantial reduction of selectivity observed. 

Cleavage of p-nitrobenzyl group. Protection of carboxylic acids and amines as the esters and carbamates can take advantage of the selective reduction-induced fragmentation by zinc dust, as C=C bonds, S-N bonds, benzyloxycarbonyl, and diphenylmethyl groups are not affected during the operation. 

Mitsunobu conditions generated 4-phosphapyrrolidone 117, which gave phosphinic acid 106 after cleavage by hydrogen of the diphenylmethyl group (Scheme 23). 4-Azaphosphinane 107 was obtained from bis(cinnamyl)phosphinate 118... 

The reactivity of the isobutyloxymethyl group towards thiocyanogen lies between that of the triphenylmethyl and the diphenylmethyl group. The difference in reactivity is not sufficient to allow the selective oxidative cleavage of the triphenylmethyl group in the presence of the isobutyloxymethyl moiety, or the cleavage of the isobutyloxymethyl group in the presence of the diphenylmethyl moiety . 

As a transient protective group, the Scm group easily replaces the Acm group or the diphenylmethyl group (eq After... 

Hydrogen bromide/formic acid Removal of N-diphenylmethyl groups Monosubst. guanidines... 

Since alkylation of 6-azauracil (4 R= H) occurs preferentially at the imide group, it is necessary to protect this in order to synthesize 6-aza analogues of uridine and related compounds. Prystas and Sorm used the diphenylmethyl group for this purpose [8]. The protected 6-azauracil (4 R=CHPh2) was... 

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