Iodo-diborane

Iodine azide, on the other hand, forms pure adducts with A -, A - and A -steroids by a mechanism analogous to that proposed for iodine isocyanate additions. Reduction of such adducts can lead to aziridines. However, most reducing agents effect elimination of the elements of iodine azide from the /mwj -diaxial adducts of the A - and A -olefins rather than reduction of the azide function to the iodo amine. Thus, this sequence appears to be of little value for the synthesis of A-, B- or C-ring aziridines. It is worthy to note that based on experience with nonsteroidal systems the application of electrophilic reducing agents such as diborane or lithium aluminum hydride-aluminum chloride may yet prove effective for the desired reduction. Lithium aluminum hydride accomplishes aziridine formation from the A -adducts, Le., 16 -azido-17a-iodoandrostanes (97) in a one-step reaction. The scope of this addition has been considerably enhanced by the recent... 

On treatment of the l-azido-2-iodo-l-methylcyclobutane (1) with diborane in tetra-hydrofuran, 2-iodo-l-methylcyclobutylamine (2) was effectively isolated in 50% yield, then lithium aluminum hydride reduction gave the same product of ring contraction 3. ... 

Nicotra et al. observed that 144 or 145, obtained by mercury-induced cycli-zation of 142 and 143, could not be converted to the desired iodo compound 146. The workers had to resort to introducing the 2-deoxynitrogen substituent after the phosphonate had been introduced as shown in Scheme 30. The ketone was converted to an oxime and with diborane gave the gluco isomer 149 in 64% diastereomeric excess [41]. 

The fully aromatic species are usually quite resistant to hydride reduction. Attempted reduction of l,2-dimethyl-5-nitroimidazole with tributyltin hydride failed to yield 1,2-dimethylimidazole <90JCS(Pl)9l9>, but the apparent reduction of 5-iodo-l-methylimidazole to l-methylimidazole by phenylsulfonylacetonitrile and sodium hydride with tetrakis(triphenylphosphine)palladium(0) as catalyst may be an example <92S552>. Lithium aluminum hydride (but not diborane) is able to convert 2-(but not 4-)fluoroimidazoles into the hydrogen species <84JOCi95i>. 

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