SELECTIVE PROPARGYLATION OF CARBONYL-COMPOUNDS WITH ALLENYLSTANNANE ALKYLLITHIUM MIXED REAGENTS

1-Substituted allenyltrialkylstannanes readily undergo transmetalation with an alkyllithium to generate a tetraalkylstannane and an equilibrating mixture of the allenyl- and propargyllithium compounds. The organolithium derivatives react with a variety of aldehydes and ketones at low temperature to give, after aqueous workup, the regioisomeric acetylenic and allenic carbinols in high yields. The degree of the regioselection is highly sensitive to the steric and electronic properties of the carbonyl substrates. Excellent acetylene selectivities are obtainable by combination of the bulky reagents and substrates or by using acylsilanes as carbonyl components. The origin of the regioselectivity is discussed. © 1990, American Chemical Society. All rights reserved.