Propargyl aldehyde cycloaddition reactions

Alkynols complexed to cobalt can be oxidized to alkynals without decomplexation. Propargyl aldehydes are protected from polymerization upon complexation with Co2(CO)6. These aldehydes smoothly undergo Wittig-type reactions. Carbonyl-ene reactions have been demonstrated (Scheme 194). Complexation to cobalt protected the enyne in complex (132) from Michael-type reactions (Scheme 195). Alkenyl-substituted complexes undergo [3 + 2]cycloadditions with nitrile A-oxides (Scheme 196). 

Winterfeldt and co-workers discovered that ergosterol acetate 35 can be used to prepare macrocycle 37 by Diels-Alder/retro-Diels-Alder reactions. Cycloaddition of ergosterol acetate 35 to propargylic aldehyde in the presence of tungsten hexachloride as a Lewis acid catalyst produced a.jS-unsaturated aldehyde 36. When it was heated in toluene, the macrocyclic benzaldehyde 37 was obtained in 85% yield (Scheme 16.5). This skeletal... 

The Brpnsted acid-mediated formal 3 + 3-cycloaddition reaction of /i-enaminones with cf, -unsaturated aldehydes formed tetrahydroquinolinones. The Yb(NTf2)3-catalysed 3 + 3-cycloaddition reaction of isatin ketonitrones (122) and cyclopropanes (123) yielded spiro[tetrahydro-l,2-oxazine]oxindoles (124) in moderate to good yields and good regioselectivities (Scheme 38). The Cu-catalysed 3 + 3-cycloaddition reaction of propargyl esters with cyclic enamines yielded chiral e r/o-adducts with bicyclo[ .3.1] frameworks. The catalyst was prepared by the combination of Cu(0Ac)2 H20 with a chiral tridentate ferrocenyl-PA(,(V-ligand. The cationic... 

Dilithio-1,3-dienes were found to react with aldehydes to form polysubstituted 2,5-dihydrofurans in a regio- and stereoselective manner <02OL2269>. Like other metal-carbene reactions, rhodium-catalyzed tandem carbonyl ylide formation - cycloaddition with propargyl bromide gave the 2,5-dihydrofuran in good yield <020L1809>. 

An important achievement is the synthesis of optically active fusicoccane, in which the key reaction is cyclization of the bis aldehyde (69). 118 Ring closure of the cobalt complex propargyl derivative (70), involving reaction via a cobalt stabilized carbocation gives access to eight-membered rings117 which are also the product of the nickel(0) catalysed [4+4]cycloaddition of the tetraene (71).118... 

Thiazolidinedione -triazole hybrids maybe synthesized by the one-pot reaction based on a Knoevenagel condensation followed by an alkyne-azide cycloaddition, between thiazolidine-2,4-dione, substituted aryl aldehydes, propargyl bromide, and substituted aryl azides using piperidine. The catalytic system is composed of CuS04 5H20 and sodium ascorbate in PEG-400 [119]. 

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