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Tripentaerythritol was converted efficiently into 2',2':6',6':10', 10'-tri-O-cyclohexylidene-2,2,6,6,10, 10-hexakis(hydroxymethyl)-4,8-dioxa-1,11-undecandiol (4) by the toluenesulfonic acid catalysed reaction with cyclohexanone in a mixture of N,N-dimethylformamide and benzene. Reaction of tripentaerythritol with benzaldehyde under similar conditions gave an easily separated mixture of the four possible stereoisomers. Structures of these stereoisomers were assigned based on ¹H and [sup.13]C NMR chemical shifts using trends previously observed for the dibenzylidene acetals of dipentaerythritol, whose structures had been established unambiguously by X-ray crystallography. It was found that reduction of the mixture of benzylidene acetals to 2,6,10-tris(benzyloxymethyl)-4,8-dioxa-1,11-undecanediol could be accomplished using triethylsilane with ethylaluminium dichloride as the Lewis acid after a number of commonly used conditions for this transformation failed. Key words: pentaerythritol, tripentaerythritol, dipentaerythritol, acetals, benzylidene acetals, reduction. La reaction du tripentaerythritol avec la cyclohexanone, en solution dans un melange de N,N-dimethylformaroide et de benzene et catalysee par l'acide toluenesulfonique, conduit a la formation de 2',2':6',6':10',10'-tri-O-cyclohexylidene-2,2,6,6,10,10-hexakis(hydroxymethyl) -4,8-dioxaundecane-1,11-diol (4). La reaction du tripentaerythritol avec le benzaldehyde dans des conditions semblables conduit a un melange des quatre stereoisomeres possibles qui ont pu etre separes facilement. Les structures de ces stereoisomeres ont ete attribuees sur la base de deplacements chimiques dans les spectres RMN du ¹H et du [sup.13]C et en faisant appel aux tendances observees anterieurement pour les acetals dibenzylidenes du pentaerythritol dont les structures avaient ete determinees sans ambiguite par diffraction des rayons X. Apres avoir essaye en vain de le faire en utilisant un certain nombre de conditions regulierement a cette fin, on a trouve qu'il est possible de realiser la reduction du melange d'acetals dibenzylidenes en 2,6,10-tris-(benzoloxymethyl)-4,8-dioxaundecane-1,11-diol en utilisant le triethylsilane en presence de dichlorure d'ethylaluminium utilise comme acide de Lewis. Mots cles : pentaerythritol, tripentaerythritol, dipentaerytrhitol, acetals, acetals dibenzylidene, reduction. [Traduit par la Redaction], Introduction Dendrimers have become the subject of intense interest in the last few years (1-7). One of the molecules that has attracted the most attention as either the central core [...]

Methods were developed to convert dipentaerythritol efficiently into di-[OMICRON]-benzylidene, di-[OMICRON]-cyclohexylidene, di-[OMICRON]-l-ethylpropylidene, and di-[OMICRON]-methylene diacetals. The known di-[OMICRON]-benzylidene acetal, considered to be a single isomer, was shown to be close to a statistical mixture of the cis, cis-,cis,trans-, and trans,trans-isomers. Structures were established by a combination of NMR spectroscopy and X-ray crystallography. Reaction of the di-[OMICRON]-benzylidene acetals with benzyl chloride and potassium hydroxide surprisingly gave good to excellent yields of the monobenzyl ethers. An explanation for this observation was advanced. The dibenzyl derivatives of the di-[OMICRON]-benzylidene acetals were formed by reaction of their dianions with benzyl bromide in DMF. Selective reduction of the di-[OMICRON]-benzylidene acetals with triethylsilane and boron trifluoride etherate gave 2',6'-di-[OMICRON]-benzyldipentaerythritol. A crown ether was formed in modest yield (12%) by reaction of the dianion of the di-[OMICRON]-methylene acetal with [alpha],[alpha]'-dibromo-m-xylene in DMF. Key words: dipentaerythritol, pentaerythritol, acetals, dendrimer, selective benzylation, crown ether.

A convergent approach is used to synthesize a nonavalent glycodendrimer bearing terminal alpha-D-mannopyranoside units and the terminal trivalent dendrons bearing p-halophenyl ethers are prepared by glycosylation of pentaerythritol derivates having three 2-hydroxyethyl ether substituents. The product was deprotected and it and its precursors were characterized by NMR spectroscopy and FT-ICR mass spectroscopy.