Propargylic alcohols hydroalumination

In this synthesis (Scheme 6), the C2-symmetri-cal triacetonide of D-mannitol (32) is converted via the epoxide 33 and its nucleophilic addition product 34 to the propargylic alcohol derivative 35. From this intermediate, the Z-configured vinyl iodide 36 is stereoselectively obtained by hydroalumination/iodination. The Pd-catalyzed Heck cyclization then affords the isomerically pure product 37, which represents a potential building block for the synthesis of la,2y5,25-trihy-droxy-vitamin D, following the classical Wittig strategy of Lythgoe. 

Alkenyl iodides can be generated in situ by hydroalumination of alkynes, followed by iodination, and a,jS-unsaturated esters are prepared by carbonylation without isolation of the iodide. As an example, the propargylic alcohol 10 was aluminated regio- and stereoselectively and converted to the alkenyl iodide 11. The intramolecular carbonylation of 11 afforded the dibutenolide 12 in 81 % yield. The reaction is a key step in the total synthesis of (-l-)-parviflorin [9]. 

Vinyl aluminium reagents 2.128 prepared by the hydroalumination of propargylic alcohols 2.127 can also undergo coupling (Scheme 2.45). This chemistry has been employed on a multigramme scale for the... 

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