Alkenes are rapidly converted to alkyl iodides under mild conditions via a hydroboration-iodination sequence which utilizes iodine monochloride as the iodinating agent. The iodination proceeds with inversion of configuration. A series of functionally substituted iodides was synthesized via the new procedure.The iodination of organoboranes in the presence of strong bases results in the regio-and stereospecific introduction of iodine in highThe utility of the I2 R3B 3R1 iodination reaction is due to the variety of functionally substituted organoboranes which are available via hydroboration.' The reaction is also important due to the variety of iodine containing radiopharmaceuticals which have been developed in recentThe iodination reaction does, however, have two potential problems. The first is the necessity of using a strong base which could either react with sensitive functional groups in complex molecules or initiate dehydrohalogenation reactions. The second is the fact that onehalf of the iodine molecule is lost as iodide which is not economical when radionuclides of iodine are employed.We report that alkenes are rapidly converted to alkyl iodides under mild conditions via a hydroboration-iodination sequence which utilizes iodine monochloride as the iodinating agent. BH3 IC1 RCH=CH2 --. -+ RCHzCHJ
Results and DiscussionWhen trialkylboranes derived from the hydroboration of terminal alkenes are treated with iodine monochloride and methanolic sodium acetate, two of the three groups on boron react instantaneously.' In the case of trialkyl-(1) Brown, H. C. "Organic Synthesis via Boranes"; Wiley: New York, (2) Brown, H. C.. DeLue, N. R. Synthesis 1976, 114. (3) Brown, H. C.; DeLue, N. R.; Kabalka, G. W.; Hedgecock, H. C., Jr. J . Am. Chem. SOC. 1976, 98, 1290. (4) Wolf, A. P.; Christman, D. R.; Fowler, J. S.; Lambrecht, R. M. "Radiopharmaceuticals and Labelled Compounds"'; M E A Vienna, 1973. (5) Counsell, R. E.; Brunswink, A.; Korn, N.; Johnson, M.; Ranade, V.; Yu, T. "Steroid Hormone Action and Cancer"; Menon, K. M. J., Reel, J. R., Eds.; Plenum Press: New York, 1976; pp 107-113. (6) Lambrecht, R. M.; Mantesen, C.; Redvanly, C. S.; Wolf, A. P. J. Nucl. Med. 1972, 13, 266.(7) It is interesting to note that the product is exclusively the l-iodoalkane even though 6% of the hexyl groups are attached to boron a t the nonterminal carbon. Obviously, primary alkyl groups migrate preferentially to secondary alkyl groups.
1975.