Allyltributyltin 2- methyl

Homoallyl ethers or sulfides.1 gem-Methoxy(phenylthio)alkanes (2), prepared by reaction of 1 with alkyl halides, react with allyltributyltin compounds in the presence of a Lewis acid to form either homoallyl methyl ethers or homoallyl phenyl sulfides. Use of BF3 etherate results in selective cleavage of the phenylthio group to provide homoallyl ethers, whereas TiCl effects cleavage of the methoxy group with formation of homoallyl sulfides. 

The fact that allyltributyltin and styrene which are electroneutral were successfully added to PCTFE led us to the question "Can electron-rich or electron-poor trapping agents be used ". The electron-rich agents that we examined were ethyl ethynyl ether and ethyl vinyl ether. On the side of the electron-poor alkenes, eight were investigated ethyl acrylate, methyl methacrylate, methyl vinyl ketone, acrylonitrile, methacrylonitrile, vinyl bromide, chloromethyl styrene, and 4-vinylpyridine. The details of each reaction are summarized. 

Adaptation of these cyclization reactions allows for the introduction of new C-C-bonded substituents so that, for example, when the bromoethyl glycoside 216 is activated with radicals generated with allyltributyltin (in place of the tributyltin hydride), the main product is the 3-C-allyl compound 218. Otherwise, branching can be introduced by carrying out the radical-promoted reactions in the presence of radical-trapping species such as methyl acrylate.218 With appropriate compounds, the initial organic radicals formed during intramolecular cyclization can be trapped by... 

Bromo-acetal 151 was subjected to tributyltin hydride promoted radical cyclization and afforded a stereoselective 8-C-methyl derivative 152. (O Scheme 40) Similarly, treatment of 151 under Keck s conditions [62] with allyltributyltin and AIBN resulted in the formation of a bis-C,C-glycoside 153 [63]. 

On the other hand, a homolytic mechanism is involved in the hydrostannation of methyl vinyl ketone in the presence of CuCl,110 and in the reaction of tributyltin hydride or allyltributyltin with cyclopropyl ketones in the presence of AIBN.14-111... 

A simple template-free methyl acrylate telomerization was conducted using the cyclohexyl iodide/allyltributyltin system in order to identify retention times for the telomers 26 from the ACT reactions. Telomerization of methyl acrylate (900 mM) with 120 mM cyclohexyl iodide and 300 mM allyltributyltin gave 27% of the n=4 telomers. Scheme 8-10. Under the best GC conditions found, only four different n=4 telomers, out of a possible 16, were observed in this product mixture. This experiment gives a baseline value for telomer distribution obtained without the use of a template. It is clear that simple template-free telomerization is not useful for the preparation of an oligomer of a specific length. 

It should be noted that the ACT sequence and the standard telomer assay were employed to study oligoselectivity with this template and thus the products analyzed are the same methyl acrylate telomers identified in the previous studies. The ACT reaction of 40 under standard conditions with cyclohexyl iodide and allyltributyltin (2.5 /80V200 "), without the aid of a counter-ion, showed interesting results. The product histogram obtained with 40 after telomer assay is presented in Scheme 8-15. 

A mixture of 4.98 g methyl 2-benzoyl-3-phenoxythiocarbonyl-4,6-benzylidene-a-D-glucoside (9.5 mmol), 7.40 mL allyltributyltin (23.9 mmol), 313 mg AIBN, and 15 mL toluene was refluxed for 4 h at which point TLC showed complete consumption of the starting material. The solution was concentrated, and the residue was flash chromatographed on silica gel using 5% EtOAc in toluene as the eluent to give 3.48 g methyl (3S)-2-0-benzoyl-4,6-di-0-benzylidene-3-allyl-3-deoxy-Q -D-glucopyranoside as a solid, in a yield of 62%, m.p. 138-139 C, Rf = 0.38 (EtOAc/hexanes, 1 9). 

C-6-Allylated pyranoses and C-S-allylated fliranoses were prepared from the corresponding iodides by Keck radical coupling with allyltributyltin (e.g. 44->4S). The selective formation of product 47 in the chain-extension of the acetal-protected uronic acid derivative 46 by radical addition of methyl acrylate using Barton s method was ascribed to addition from the less hindered side to a conformationally stable radical intermediate the peracetate 48 furnished a 1 1 mixture of 49 and 50. ... 

Radical reactions have been further utilised in the construction of branched-chain sugars. Unsaturated iodide (24) with allyltributyltin or Bu3SnH and methyl acrylate has afforded the doubly-branched derivatives (25) and (26) by way of intra- and then inter-molecular radical processes. Similarly, bromide (27) gave the 3-C-allyl derivative (28) which, after transformation into enal (29), underwent a further radical cyclisation (Scheme... 

---