Dichloroaluminum hydride

Ethyl (Z)-2-bromomethyl-2-heptenoate and aldehydes condense on reaction with chromium(II) chloride to furnish cw-3,4-disubstituted dihydro-3-methylene-2(3 //)-( uranones exclusively16, indicating that a (Z)-allylchromium complex might serve as reactive intermediate in the. mv-selec-tive addition step due to the bulky 2-substitucnt. Alternatively, an acyclic transition state for the reaction of the ( )-diastereomer, mediated by the Lewis acid dichloroaluminum hydride, has been discussed16. 

This approach makes use of bromopropyl phosphine 17 as a key synthon obtained via the reduction of 3-bromopropyl phosphonate with dichloroaluminum hydride [10]. Reaction of bromopropyl phosphine 17 with the dianion of 6,8-dithiooctanoic acid produced the -COOH functionalized P2S2-primary bisphosphine framework 18 in > 80% yields (Scheme 7) [10]. 

Surprising results have been encountered in the hydrogenolysis of enamines to alkenes in the course of their reduction with an 1 1 mixture of lithium aluminum hydride and aluminum chloride in ether.301 From 1-pyrrolidinocyclopentene, 83% of cyclopentene was thus obtained. Formation of a-pyrrolidinocyclopentylaluminum chloride on addition of monochloroaluminum hydride to the enamine must be postulated, followed by decomposition of the intermediate complex to the cyeloalkene. The single known instance of reduction of a free enamine is represented by the reaction with dichloroaluminum hydride.302 Addition of the reagent leads to a complex which, on decomposition with water, affords the saturated base (Scheme 12). 

Aluminum hydride, AIH3, and dichloroaluminum hydride, CI2AIH, can be obtained as etherates by the original method of Schlesinger and coworkers and can be employed for hydroalumination (equation 8).2 ... 

Azetidin-2-ones are reduced chemoselectively by diisobutylaluminum hydride or by chloroaluminum and dichloroaluminum hydrides in tetrahydrofuran (THF) to form azetidines [17]. 

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