@article{HernandezTorres:2004:J-Org-Chem:15471470,
	title = {Temperature-controlled regioselectivity in the reductive cleavage of p-methoxybenzylidene acetals},
	author = {J M Hern{\'a}ndez-Torres and J Achkar and A Wei},
	journal = {J Org Chem},
	month = {Oct},
	number = {21},
	pages = {7206-7211},
	url = {http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1851890},
	volume = {69},
	year = {2004},
	biburl = {http://www.bibsonomy.org/bibtex/2efeb499ae33de69618216e525973541e/rstenutz},
	abstract = {The regioselective ring opening of pyranosidic 4,6-p-methoxybenzylidene acetals with BH(3)/Bu(2)BOTf in THF can be tuned by adjusting the reaction temperature and reagent concentrations. Reductive cleavage at 0 degrees C resulted in the exclusive formation of 4-O-p-methoxybenzyl (PMB) ethers, whereas reaction at -78 degrees C produced 6-O-PMB ethers in high yields. The latter condition was observed to be compatible with a variety of acid-sensitive functional groups, including allyl and enol ethers. The presence of water does not interfere with reductive ring opening and may contribute toward in situ generation of H(+) as a catalyst for 6-O-PMB ether formation. Reductive cleavage under rigorously aprotic conditions is greatly decelerated, and yields only the 4-O-PMB ether. The temperature-dependent reductive cleavage of the 4,6-acetal can be described in terms of kinetic versus thermodynamic control: Lewis-acid coordination of the more accessible O-6 is favored at higher temperatures, whereas protonation of the more basic but sterically encumbered O-4 predominates at low temperatures.},
	pmid = {15471470}, doi = {10.1021/jo048999m},
	keywords = {benzylidene carbohydrate synthesis }
}