Carbonylative annulations, 3- bromide

The [4+1] annulation of 1-azadienes to pyrroles can also be achieved through their carbonyl iron complexes (Scheme 6). Novel complex (1,4-diphenyl-2-methyl-l-azabutadiene)tricarbonyliron (0) 24 was obtained in 40% yield from the corresponding azadiene 23 and Fe2(CO)9 then nucleophilic attack by methyl lithium and quenching with tert-butyl bromide, as the proton source, gave 2,5-dimethyl-l,3-diphenylpyrrole 26 in 70% yield, probably through the anionic intermediate complex 25 [88TL1425 90JCS(P1)761]. 

Sequential nucleophilic and electrophilic alkylations of 1,3-dicarbonyl compounds with a trimethylenemethane zwitterion equivalent lead to [3 + 2]-annulation. The nucleophilic carbonyl alkylation step has been carried out via an indium-mediated allylation in water (Equation (30)).200 Indium-mediated allylation of a-chlorocarbonyl compounds with allyl bromides in aqueous media gives the corresponding homoallylic chlorohydrins, which can be transformed to allyloxiranes (Equation (31)).201 Allylation of the G3 position of the cephem nucleus has been accomplished by indium-mediated allylation reaction in aqueous media (Equation (32)).202... 

Annulation of a phosphontum salt and the carbonyl of an acyloxy group (formed in situ) proceeds in good yield on heating with TEA. High yields of benzofurans (review of recent work on benzofurans [3894]) are obtainable by heating a mixture of the a-hydroxybenzylphosphonium bromide, an acyl halide and TEA in toluene. 

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