Reductive cyclization Triphenyltin hydride

On treatment with benzeneselenenyl chloride two olefinic urethanes (214 and 217) underwent cyclization to afford piperidine derivatives (215 and 218, respectively) having the cis stereochemistry. Their reduction with triphenyltin hydride gave the same product (216). Removal of the blocking group from the nitrogen gave ( )-isosolenopsin A (Ic) (Scheme 6) (392). 

It is important to emphasize that the hydroxy dithioketal cyclization can be conducted under mild reaction conditions and can be successfully applied to a variety of substrates.15 However, the utility of this method for the synthesis of didehydrooxocane-contain-ing natural products requires the diastereoselective, reductive removal of the ethylthio group. Gratifyingly, treatment of 13 with triphenyltin hydride and a catalytic amount of the radical initiator, azobisisobutyronitrile (AIBN), accomplishes a homolytic cleavage of the C-S bond and furnishes didehydrooxocane 14 in diastereo-merically pure form (95 % yield), after hydrogen atom transfer. 

John and coworkers78 also observed cyclization to a five-membered ring heterocycle in their hydride reduction of methyl 6/i-isothiocyanatopenicillanate with both tributyltin hydride and triphenyltin hydride (Scheme 16). John and coworkers also found this type of ring closure when an isocyanide was reduced with tributyltin deuteride. The mechanism of this arrangement (Scheme 17) has been confirmed by deuterium labelling. 

Reductive coupling of carbonyls to alkenes Titanium(IV) chloride-Zinc, 310 of carbonyls to pinacols Titanium(III) chloride, 302 Titanium(IV) chloride-Zinc, 310 of other substrates Samarium(II) iodide, 270 Reductive cyclization 2-(Phenylseleno)acrylonitrile, 244 Tributylgermane, 313 Tributyltin hydride, 316 Triphenyltin hydride, 335 Trityl perchlorate, 339 Reductive hydrolysis (see Hydrolysis) Reductive silylation Chlorotrimethylsilane-Zinc, 82... 

In the final stages of the synthesis (Scheme 21), the dimerization protocol developed earlier (Scheme 5, vide supra) was followed, with the slight modification that triphenyltin hydride was used for reduction of the azide functional group. Cyclization of the a-aminoketone with PPTS afforded dimer 46 in 79 % yield, accompanied by 17 % of deazidoketone monomer. Removal of the... 

Reductions of carbon-halogen bonds are initiated similarly. In this case, several tin hydrides (di- and tributyl, triphenyl) can be used with practically equal effectiveness. lododecane gives the hydrocarbon in 88% yield after sonication for 2 h with triphenyltin hydride in THF at - 64°C. An equivalent yield is obtained using the tributyl analogue in toluene at 6°C. With substrates containing an unsaturation in a suitable position, cyclization occurs (Eq. 9). Interception by oxygen of the intermediate radical can be stopped at the hydroperoxide stage. 4... 

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