Propargyl alcohols, cyclocarbonylation reactions

In 1991, El-Ali and Alper reported the cyclocarbonylation reaction of terminal propargyl alcohols with formation of 5,5-disubstituted 2(5//)-furanones using Pd(dba)2 and l,4-bis(diphenylphosphino)butane (dppb) (91JOC4099). However, this reaction was not applicable to internal alkynols. 

Substituted propargylic alcohols were found to undergo direct carbonylation to the corresponding butenolides in 67-98% yield (Eq. 9.120) [86]. This reaction requires a catalytic amount of Pd2(dba)3-CHC13 (4%) and l,4-bis(diphenylphosphi-no)butane (8%) in CH2C12 under an atmosphere of CO (600 psi) and H2 (200 psi) at 95 °C for 36 h. The cyclocarbonylation reaction is believed to proceed via an allenyl-palladium intermediate, which is formed by initial insertion of Pd(0) into the C-O bond of the alkynol followed by rearrangement (Scheme 9.25). 

The PdCb-catalysed cyclocarbonylation of propargylic amines (70) with CuCl2 and p-benzoquinone afforded ( )-o -chloroalkylidene-/3-lactams (71) in moderate to good yields. The formation of the corresponding Z-isomers or five-membered ring products was not observed. The stereoselectivity in this reaction is different from that observed with propargylic alcohols a mechanistic rationale has been proposed.83... 

The reaction was successfully extended to the hydroformylation of propargyl-type alcohols [154] and propargylamine [155], the silylative cyclocarbonylation of alkynes [156], silylcarbocyclization of alkenynes and diynes [157-160], and other transformations of C=C bonds in the presence of HSiRa and CO (e. g., [161]). A generalized catalytic cycle for the silylformylation of 1-alkynes catalyzed by rhodium-cobalt clusters is illustrated in Scheme 6. 

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