This paper reports some studies aiming at the developement of a general protocol useful for the synthesis of allyl-and prenylaromatic compounds. The first part deals with the preparation of boron reagents like arylboronic acids and their pinacol esters as well as of pinacol allyl-and prenylboronates. The second part of the paper is devoted to the use of these boron reagents in Suzuki-Miyaura cross-coupling reactions leading to allylation and prenylation of aromatic compounds. Of the six methods studied, the most promising re- IntroductionThe selective formation of new carbon-carbon bonds is frequently a key step in the synthesis of molecules of high added value, like fine chemicals, as well as in the preparation of conventional and special polymers. Cross-coupling reactions catalysed by metal complexes could undoubtedly be included among the most powerful and versatile synthetic methods for achieving these transformations.[1] During the last 30 years, the development of a wide variety of cross-coupling methods has facilitated the synthesis of carbon-carbon bonds between unsaturated species, notably sp and sp 2 moieties, like vinyl, alkynyl and phenyl groups. Of the coupling reactions catalysed by palladium, the SuzukiMiyaura reaction, that is, the reaction between organoboron compounds and organic electrophiles, for example, vinyl, alkynyl, aryl and benzyl halides and triflates, catalysed by palladium complexes (Scheme 1) is one of the most useful for making carbon-carbon bonds.[2] The first example of this protocol was reported by Suzuki and coworkers in 1979. [3] Some of the advantages of this reaction are the availability of a wide variety of reagents, mild reaction conditions, the compatibility of boron derivatives with a wide range of functional groups and their lower toxicity compared with [a] other organometallic derivatives, for example, organotin compounds. In addition, inorganic boron byproducts have a low environmental impact, minimal toxicity and can be removed by very simple procedures. On the other hand, taking into account the fact that allylation and prenylation reactions are useful tools for the introduction of chains containing carbon-carbon double bonds leading to fragments that in many cases are part of natural products, [4,5] it would certainly be of interest to find more general techniques for carrying out these reactions. Although successful allylation and prenylation reactions of a wide variety of organic substrates by cross-coupling reactions have been reported, [5a,5b,6] in most cases the protocols of these reactions could only be applied with excellent yields to particular systems and not in general. Also, surprisingly, the nature of the organoboron coupling partners has been little studied. Owing to the importance of these reactions in synthetic applications, we considered it of interest to carry out a study to establish both the conditions and methods needed to develop a protocol that could be applied successfully to the allylation and prenylation of a wide number of organic substr...

This paper reports the results obtained in a study on the radical addition of triorganotin hydrides, R 3 SnH (R ) Me, n-Bu, Ph; Neophyl), to four TADDOL unsaturated diesters. It was found that these reactions lead in high yields to products of cyclohydrostannation. It was also found that whereas the addition of these hydrides to TADDOL diacrylate and TADDOL dimethacrylate leads to the expected mixtures of two and four cycloundecane diastereoisomers, respectively, the addition of triphenyltin hydride to TADDOL disubstituted acrylates yields only four out of the 16 possible stereoisomers. The observed high stereoselectivity is consistent with the radical tandem cyclohydrostannation mechanism proposed. Only in the case of the hydrostannation of TADDOL diacrylate with trimethyl-and triphenyltin hydrides could the diastereoisomers obtained in higher proportion (5a and 8a) be isolated in pure form. The subsequent reduction (lithium aluminum hydride) of macrolides 5a and 8a afforded the corresponding optically active diols 26 and 27 in high yield. Full 1 H, 13 C, and 119 Sn NMR data are given.

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