Pergamon Tetrahedron Letters, Vol. 38, No. 44, pp. 7681-7682, 1997 © 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain qnnAn_An~nln'7~,nnnn_, 0040-4039/97 $17,00 + 0.00 Pn: ~..~u~Ptu '-I.uj ) ~7/) i I, dnLpt/~- i Selective Hydroboration of Unconjugated Alkynyl Ketones and Aldehydes George W. Kabalka,* Su Yu and Nan-Sheng Li Departmentof Chemistry;The Universityof Tennessee Knoxville, TN 37996-1600 Abstract: Unconjugated alkynyl ketones and aldehydes are selectively hydroborated to give the corresponding olefinic carbonyl compounds after protonation, or dicarbonyl compounds after oxidation. © 1997 Elsevier Science Ltd. Hydroboration of alkenes and alkynes has been utilized extensively in organic synthesis. ~ The hydroboration of substrates containing carbonyl groups is often carried out by either converting the carbonyl group to a less reactive functionality 2 or modifying the hydroborating agent 3 to avoid reduction of the carbonyl group 4 even though kinetic studies involving disiamylborane suggested that these approaches might not be necessary, s Recently, we reported that terminal alkenes could be selectively hydroboreted in the presence of ketones and aldehydes.6 We now wish to report the selective hydroboration of unconjugated alkynyl ketones and aldehydes. o O ~ NaBO3 O O = ~ (76%) A variety of unconjugated alkynyl carbonyl compounds were hydroborated with dicyclohexylborene. The results are summarized in the Table. Both terminal and internal alkynyl carbonyl compounds could be selectively hydroboroated in the presence of the carbonyl group. The reaction affords the corresponding olefins in high yields (71-94%) after protonation, or the dicarbonyl compounds in good yields (50-76%) after oxidation with sodium perborate, z The hydroboration of 11-dodecyn-2-one is representative: BH3-THF (2.0 mmol, 2.0 mL of a 1.0M solution in THF) was placed in a dry, argon-flushed flask which was then immersed in an ice-water bath. Cyclohexene (4.0 mmol, 0.33g, 0.41 mL) was added dropwise and the mixture stirred at 0 °C for 1 hour. 11-Dodecyn-2-one (2.0 mmol, 0.36 g) was then added to the slurry of dicyclohexylborane in THF. The cooling bath was removed and the mixture stirred for 1 hour at room temperature. Protonation was achieved by adding glacial acetic acid (1 mL) and stirring 7681