Acyl hypoiodites

Bridgehead carboxylic acids, e.g. adamantane-1-carboxylic acid, are transformed into acyl hypoiodites, followed by photochemical decarboxylation to yield the corresponding bridgehead iodides1091. 

An alternative method for the formation of acyl hypoiodites, developed by Barton, involves the treatment of the acid with r-butyl hypoiodite. Subsequent white light photolysis in benzene at room temperature gave good yields of it ides from primary, secondary and tertiary acids (equation 21). The method was not applicable in the presence of alcohols. A more recent technique involving hypervalent iodine is due to Suarez primary, secondary or tertiary aliphatic acids are heated to reflux in tetrachloromediane with iodosylbenzene diacetate and iodine resulting in good yields of iodides. The method is mild and, with obvious exceptions such as unprotected alcohols, is tolerant of many functional groups, as illustrated in equation (22). ... 

Acyl hypoiodites e.g. 21), generated from carboxylic acids (30) by the action of lead tetraacetate and iodine, or of tert-bxityl hypoiodite, undergo decarboxylation by visible light to give alkyl iodides [6y]. The reaction is formulated as a... 

Britten-Kelley, M. R., Goosen, A., Scheffer, A. Kinetic studies on the photodecarboxylation reactions of acyl hypoiodites. J. S.African Chem. Inst. 1975, 28, 224-234. 

Decarboxylation. A benzene solution of a carboxylic acid and f-butyl hypoiodite presumably contains an equilibrium amount of r-butanol and the acyl hypoiodite, which on illumination decomposes to the alkyl iodide and CO ... 

The fourth modification of the Hunsdiecker reaction, pioneered by Barton, is the use of /-butyl hypoiodide.23 Thus, acid 16 was treated with /-butyl hypoiodide to give the acyl hypoiodite, which underwent white-light photolysis at room temperature to give iodide 17. The reaction works for primary, secondary, and tertiary acids. 

For the preparation of iodoacetylenes the alkali hypoiodite may be replaced by an acyl hypoiodite in the form of a Simonini complex, [(C6H5COO)2Ag]I. 

Kato, M., M. Kageyama, R. Tanaka, K. Kawahara, and A. Yoshikoshi Synthetic Study of ( )-Canadensolide and Related Dilactones. Double Lactonization of Unsaturated Dicarboxylic Acids via Acyl Hypoiodite Intermediates. J. Organ. Chem. (U.S. A.) 40, 1932(1975). 

Courtneidge, J.L., Lusztyk, J., and Page, D., Alkoxy radicals from alcohols. Spectroscopic detection of intermediate alkyl and acyl hypoiodites in the Suarez and Beebe reactions. Tetrahedron Lett., 35, 1003, 1994. 

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