Abstract:

Carbonyl propargylation or allenylation by 3-haloprop-1-yne with metal or metal salts is one of the most convenient methods for introduction of propargyl(prop-2-ynyl) or allenyl functions which can be transformed into natural products and pharmaceutical intermediates. Currently, the Barbier-type propargylation of aromatic adehydes mainly focuses on the active metal indium or its salt, and the solvents used are generally THF or THF/H₂O mixture. In comparison, there are a few reports about the propargylation of carbonyl compounds promoted by metal tin or its salts in pure water. Additionally, due to the reaction regioselectivity, there are two competitive products such as homopropargylic alcohol and allenyl alcohol. Hence, it is worth to explore the highly efficient protocol for the preparation of single product. Based on our work on the allylation of carbonyl compounds and the application of homopropargylic alcohol, we herein attempt to study the propargylation of carbonyl compound so as to conveniently obtain excellent yields of homopropargylic alcohol which is used as the further reaction substrate. Therefore, this paper reported a simple, highly efficient and fast protocol for the propargylation of aldehyde. Namely, employing inexpensive metal tin powder, the Barbier-type propargylation of aldehydes can be achieved with the Lewis acid SnCl₂·2H₂O as additive, and then affording the single homopropargylic alcohol with high yields and high regioselectivity(up to 99% yield). Moreover, this methodology had some obvious advantages such as broad substrates applicability, mild reaction condition(30℃), environmentally benign(water media), rapid(the reaction raw materials can nearly disappear in 30 min) and so on. In addition, in the case of cinnamic aldehyde substrate, a novel enyne ether with highly symmetric structure was unexpectedly obtained when the reaction was carried out at an increasing temperature of 55℃.

Key words: Metal tin, Aqueous media, Aromatic aldehyde, Propargylation