Alkylated organotin derivatives

Tin-based reagents are not always snitable owing to the toxicity of organotin derivatives and the difficulties often encountered in removing tin residues from the final product. Therefore, the same authors have carried out additional experiments with 17d and several different alkyl halides under tin-free conditions. The treatment of 16d with tert-butyldiphenylsilyl chloride (TBDPSCl) and triethylamine in the presence of silver triflate in CH2CI2 affords the bis(silyloxy)enamine 17d in 92% yield (Scheme 17). When the radical reaction was carried out with ethyl iodoacetate in the presence of 2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as the initiator in CH2CI2, the oxime ether 19 was obtained in 83% yield (Scheme 17). 

Before workup of the reaction of the dibutylstannylene acetal of a diol with an electrophile such as an acyl, alkyl, or sulfonyl halide, the product present in nonpolar solvents has a halodibutylstannyl group attached to the nonreacted oxygen atom. This organotin derivative can be cleaved with water or mild acid, but chromatography on silica gel is usually sufficient to remove it. Some research groups have made use of the strong Sn-F bond by washing with fluoride ions. 

As in the case of benzylation, strategies used for selective allylation include prior conversion to organotin derivatives. When comparisons have been made, there does not seem to be significant differences in selectivities between benzylation and allylation [33,78]. Diols have also been selectively alkylated as their copper (II) salts. Under such conditions no disubstitution is observed and regioselectivity towards formation of a preferred monoallylated product (4,6-diols give mainly 4-substitution and 2,3-diols give mainly 3-substitution) is usually high (O Scheme 11) [79]. 

Direct methylation with diazomethane [154] or alkylation of organotin derivatives of uridine 64 lead to non 2 -0-selective alkylations. The organotin approach using alkyl halides and temperatures up to 130 °C leads to the formation of equal amounts of 2 - and 3 -0-alky-luridines, which may be separated by chromatography after dimethoxytritylation. Alkylation of the uracil moiety does not occur with this method. Purification of the isomeric mixture may be achieved after further derivatization [155]. 

The manufacture of OTC involves a two-step reaction. The first step can be achieved in a number of different ways and involves reaction of tin tetrachloride (SnCU) with a suitable reagent to produce various tetraalkyltin compounds (ILjSn). In the second step, It Sn reacts with SnCU in a redistribution reaction to form less alkylated organotin chlorides such as R3SnCl, R2SnCl2, or RSnCls. From these products, various other tin derivatives can be produced. A direct reaction scheme is also possible whereby the organotin halides can be synthesized by a reaction between tin metal or alloy and alkyl halides. 

A review on the regioselectlve manipulation of hydroxy groups via organotin derivatives has covered regioselectlve alkylation,... 

Some new inositol ethers (6) - (10) with liquid crystalline behaviour have been prepared from myo-inositol. and a symposium has reported on the use of 4-nitiobenzyl and 4-pivaloylaminobenzyl groups for the protection of hydroxyl groups in the synthesis of complex carbohydrates. A modified procedure whereby the 3-0-alkylation and 3-0-benzylation of methyl a-D-manno-, a-L-rhamno- and L-fuco-pyranoside can be effected directly in good yield via organotin derivatives has been described. ... 

Use of mild conditions was crucial and the development of diimide reduction of singlet oxygenates, silver-salt-assisted displacement of halide by peroxide nucleophiles, peroxymercuration and demercuration, peroxide transfer from organotin to alkyl triflates, and oxygen trapping of azoalkane-derived diradicals have all played a part in providing the rich harvest of new bicyclic peroxides described herein. 

Iodomethyltrialkyltin compounds, R3SnCH2I (from R3SnCl and ICH2ZnI), provide an entry to other functionally substituted organotin compounds. Reaction with nucleophiles such as R10, R1S, R 2N, or R 3P gives further a-substituted derivatives, and carbon nucleophiles can be used to locate the functional groups at more distant positions on the alkyl chain. Some examples are shown in Scheme 3. 

The diprotic porphyrins, H2(Por) 63, give rise to organotin(iv) derivatives, R2Sn(Por) or RXSn(Por) (X = halide) Por represents a generalized porphyrin dianion, often with alkyl or aryl substituents in the peripheral positions. 

Metallated polystyrenes are versatile intermediates for the preparation of a number of polystyrene derivatives. Metallated polystyrene has been prepared from haloge-nated polystyrenes by halogen-metal exchange [41,42,65,66] and by direct metallation of polystyrene [67-69] (see Chapter 4). Electrophiles suitable for the derivatization of metallated polystyrene include carbon dioxide, carbonyl compounds, sulfur, trimethyl borate, isocyanates, chlorosilanes, alkyl bromides, chlorodiphenylphosphine, DMF, oxirane, selenium [70], dimethyldiselenide [71], organotin halides [69], oxygen [72], etc. [41,42,65-67],... 

---