Hydroformylation acetals

Table 35 Homogeneous WGS, hydroesterification, hydroformylation-acetalization rates for cw-[Rh(CO)2(amine)2PF6 over 4 hours174... 

Very recently the tandem hydroformylation/acetalization has been used for the synthesis of new synthetically valuable chiral auxiliary derived from camphor. Stereoselective allylation of camphor and subsequent terminal hydroformylation of the resulting homoallylic alcohol affords the 5-lactol auxiliary (camTHP OH) in multigram scale (Scheme 8) [41]. 

Rhodium-catalyzed tandem hydroformylation-acetalization of a,co-alkenediols is a facile entry to perhydrofuro[2,3-6]furans. A benzoannulated tetrahydrofuro[2,3-fc]furan was obtained in this manner <02OL289>. A mixture of trisubstituted tetrahydrofurans was obtained from a n-allylmolybdenum complex and this is depicted in the following scheme <020L2001>. 

Eilbracht et al. by means of rhodium-catalyzed tandem hydroformylation/acetalization of cccw-alkenediols [20]. It had been previously reported that hydroformylation of alkenol resulted in cyclic hemiacetal [21]. Starting from enediols, the authors paved the way for subsequent acetalization, leading to fused bicyclic compounds in a one-pot cascade. As expected, exclusive formation of czs-fused perhydrofuro[2,3fr]furan 6 occurred when applying 60 bar of syngas (CO H2 = 3 1) at 120 °C in dichloromethane to diol 5 in the presence of a [Rh(cod)Cl]2/PPh3 catalytic system (Scheme 4). 

A tandem hydroformylation/acetalization reaction of/r-menthenic terpenes in the absence of an acid co-catalyst was reported by Vieira et The reaction took place in ethanol solution in the presence of PPhsor P(0-o-BuPh)3. 

Typical procedure forthe tandem hydroformylation-acetalization reaction of terpene ... 

Unexpectedly, the 3,4,6-tri-O-benzyl-D-glucal gave only the methyl a-glycoside 121 under the hydroformylation-acetalization conditions. In fact, there are two electrophilic reagents in competition for the nucleophilic alkene, the rhodium complex and the proton. When the alkene is deactivated (R=Ac) the coordination of rhodium is preferred and the hydroformylation-acetalization takes place. But when it is not deactivated (R=Bn) the acidic proton reacts faster than rhodium and methanol is added. 

Scheme 4.8 Manufacture of fuel additives through hydroformylation/acetalization from renewable resources.

Scheme 5.68 Principle of hydroformylation-acetalization reaction and a typical side reaction.

Consecutive hydroformylation-acetalization reaction can be achieved either by the proper choice of a single catalyst, which assists in both reactions (1), or by the utilization of two different catalysts (2), the first for the hydroformylation and the second for the acetalization (Scheme 5.69). Because of the taxonomy of Fogg and dos Santos [4], the first approach can also be termed auto-tandem catalysis. 

Scheme 5.69 Types of hydroformylation-acetalization tandem reactions.

---