Hydrostannolysis

O Dangles, F Guibe, G Balavoine, S Lavielle. A Marquet. Selective cleavage of the allyl and allyloxycarbonyl groups through palladium-catalyzed hydrostannolysis with tributyltin hydride. Application of the selective protection-deprotection of amino acid derivatives and in peptide synthesis. J Org Chem 52, 4984, 1987. 

This chemistry forms the basis of a general method for 1,3-hydroxy transposition in allylic alcohols (equation 7). The starting alcohol is converted by 3,3-sigmatropic rearrangement of the 0-allyl-S-methyldithiocarbonate followed by hydrostannolysis to the allylic stannane, which is oxidized by MCPBA in a completely regiospecific manner. A similar sequence has been reported for allylsilanes. "... 

The synthesis of tristannanes and linear tetrastannanes can be achieved in a straightforward manner by employing the hydrostannolysis reaction and diorganotin dihydrides (26) and 1,1,2,2-tetraorganodistannanes (9) according to Eq. (8) 49). As shown, this methodology can be used to... 

In addition to the hydrostannolysis reaction, another procedure that has been used for the synthesis of tristannanes, such as compound 39, is through the reaction of the triorganotin anions, R3SnLi, with diorganotin dihalides according to Eq. (9) in Scheme 8. This method has also been... 

Experimental procedures for the cleavage of V -Aloc derivatives on resin by palladium(O)-catalyzed hydrostannolysis are reported in Section 4.3.2.S.2. 

N -Protection as allyl carbamate is used generally only for specific synthetic purposes where acid- or base-mediated deprotection procedures must be avoided or reduced to a minimal extent as in the case in the synthesis of glyco- and phosphopeptides (see Sections 6.3 and 6.5). Otherwise the orthogonality of this type of amino protection has been mainly exploited in side-chain protection to allow for selective chemistry such as selective acylations, e.g. cyclizations, to be performed on protected peptides in solution or in the resin-bound state (see Section 4.3.2.3.4). An additional interesting application of the Aloe group is the one-pot deprotection and acylation with carboxy components resistant to the paUadium(0)-catalyzed allyl cleavage by hydrostannolysis as reported in Section 4.3.2.3.4.P 1... 

Aloe Deprotection by Palladium-Catalyzed Hydrostannolysis (Synthesis of Substance... 

When deprotection reactions of the Aloe group with a palladium catalyst and pseudometallic hydrides, namely tributyltin hydride, sodium borohydride, or phenylsUane, are performed in the presence of an acylating agent, the deprotected amino group is directly obtained in its acylated form.P This tandem deprotection-acylation reaction is believed to involve a concerted decarboxylative condensation of the initially formed pseudometallic carbamate with the acylating agent, as represented in Scheme 8 in the case of hydrostannolysis.t ... 

Scheme 8 Tandem Deprotection-Aminoacylation by Hydrostannolysis in the Presence of an Acylating Re-agentP l...

A113. H. M. J. C. Creemers, Hydrostannolysis. A General Method for Establishing Tin-Metal Bonds. Schotanus and Jens, Utrecht, 1967. 251 pp. 

Most of these compounds are prepared by the hydride method, by hydrostannolysis of metal alkyls with organotin hydrides (see 5.7.5.2). 

Most Sn—Zn bonds are prepared by the hydride method, i.e., hydrostannolysis using an organotin hydride and a dialkylzinc or alkylzinc halide, either complexed or uncomplexed. 

The reaction of EtjSnH with EtjZn results in decomposition with the formation of Zn metal, ethane, tetraethyltin, hexaethylditin and a polymerp The reaction of PhjSnH with EtjZn in pentane or benzene forms metallic Zn. However, when hydrostannolysis is carried out with preformed complexes of Et2Zn or with a complexing solvent, such as 1,2-dimethoxyethane (DME) or tetrahydrofuran (THE), or by using a preformed coordination complex of EtjZn with tetramethylethylenediamine (TMED) or bipy, the bis(triphenyltin)zinc complexes are obtained in high yields under mild conditions (—20° to 0°C)2 ... 

When EtZnCl is used instead of Et2Zn in these hydrostannolyses with Ph3SnH, and under the same conditions, selective hydrostannolysis of the Zn—C bond occurs to form (triphenyltin)zinc chloride complexes (see Table 1) ... 

Whereas attempts to prepare (trialkyltiti)zincs by hydrostannolysis of ethylzincs by trialkyltin hydrides fail, MePhjSnH yields such compounds from Et2Zn-TMED and EtZnCl- ... 

A thermally stable neopentylstannylcadmium is obtained by hydrostannolysis of EtjCd with the corresponding organotin hydride at 20°C for 2 h ... 

When t-Bu2Hg reacts with trialkyltin hydrides at 30°C hydrostannolysis occurs yielding the corresponding (R3Sn)2Hg ... 

In 1962, Kuivila showed that the reaction of trialkyltin hydrides with alkyl halides (hydrostannolysis) (equation 1-6) was a radical chain reaction involving short-lived trialkyltin radicals, R3Sn, 12 and in 1964, Neumann showed that the reaction with non-polar alkenes and alkynes (hydrostannation) (equation 1-7) followed a similar mechanism,13, 14 and these reactions now provide the basis of a number of important organic synthetic methods. 

Scheme 15-2 Homolytic chain mechanisms of hydrostannolysis and hydrostannation.

In recent years, these reactions have found an important place in organic synthesis. We will consider in this chapter only the reactions of radicals with tin hydrides, and the basic hydrostannolysis processes that depend on these reactions. Hydrostannation reactions are covered in Section 4.4, and the reactions of stannyl radicals with substrates R X in Section 20.1.3. The further use of organotin hydrides in organic synthesis, which depends largely on transformations of the radicals R " in hydrostannolysis reactions, or of the radicals R3SnXY" in hydrostannation reactions, are beyond the scope of this book, but have been extensively reviewed.2 64 66 104 107... 

The hydrostannolysis of organic halides was discovered when an attempt at the hydro-stannation of allyl bromide resulted instead in hydrodebromination.37... 

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