Hydroformylation/allylboration domino reactions

Hydroformylation reactions have been shown to be amenable to use in tandem or domino reaction sequences. In one elegant example, alkene 36 was subjected to rho-dium(I)-catalyzed hydroformylation, and the resulting aldehyde underwent smooth intramolecular allylboration (Scheme 5.14) [19]. This produced a new terminal alkene which underwent a second hydroformylation to provide, after workup,lactols 37 in 80% yield and with excellent diastereoselectivity. 

Intramolecular Allylboration. In one rare but impressive example involving a masked aldehyde, a domino hydroformylation/allylboration/hydroformyla-tion reaction cascade has been designed to generate bicyclic annulated... 

Abstract Intramolecular allylboration of a>oxo-2-alkenylboronates allows the stereoselective formation of 2-vinyl-cycloalkanols. When heteroatoms are present in the chain linking the aldehyde and allylboronate functions a variety of saturated heterocycles with a stereodefined pattern of substituents may be prepared in this manner. Rapid assembly of anellated heterocycles becomes possible by domino-hydroformylation-allylboration-hydroformylalion cascade reactions. 

The successful completion of this domino reaction encouraged us to check some further hydroformylation-allylboration-hydroformylation sequences. For instance, the homoallylic alcohol 58 was converted to the ynol ether 59. To convert the latter to the alkenyl boronate (55%) 60 a zirconium catalyst (30) had to be chosen for the hydroboration. With rhodium catalysts chemoselectivity between the alkyne and the alkene moieties was... 

---