Allyl ethers hydroformylation

McDonald RI, Wong GW, Neupane RP, Stahl SS, Landis CR (2010) Enantioselective hydroformylation of N-vinyl carboxamides, allyl carbonates, and allyl ethers using chiral diazaphospholane ligands. J Am Chem Soc 132 14027-14029... 

Polo A, Claver C, Castillon S, Ruiz A, Bayon JC, Real J, Mealli C, Masi D (1992) Regioselective hydroformylation of cyclic vinyl and allyl ethers with rhodium catalysts. Critical influence of the size of the phosphorus cocatalyst. Organometallics 11 3525-3533... 

Systematic studies on the influence of temperature on the regioselectivity in the hydroformylation of vinyl substrates in the presence of unmodified rhodium-hased precursors have been carried out only in few cases. In particular the investigations reported in literature concern the hydroformylation of styrene, ethyl- and allyl ethers and 1-hexene, with RJi4(CO)i2 over temperatures, ranging from 20 °C to 100 °C. 

The hydroformylation of 2,3-dihydrofuran and 3,4-dihydro-2//-pyran can be accompanied by partial isomerization to the isomeric cyclic allyl ethers. In general, dihydrofurans as substrates require conditions milder than those used for dihydropyrans, which has been explained by the more planar structure of the five-membered ring that facilitates the formation of substrate-metal complexes [17]. 

Scheme 4.36 Isomerization and hydroformylation of cyclic allyl ethers.

The hydroformylation of allyl ethers with cumenyl, isobornyl, 2-methyl-2-pentanol, and terpinyl groups was patented by IFF (Table 6.4) [186]. In all cases, the linear and branched aldehydes were formed. After distillation, the odors of the linear compounds were evaluated. The isobornyl-derived aldehyde was reduced to give a corresponding hydroxy butylether with a typical patchouli aroma. 

Table 6.4 Hydroformylation of allyl ethers and perfumery properties.

Production of Aroma Compounds and Fragrances via Fiydroformylation 575 Table 6.5 Hydroformylation of branched allyl ethers and perfumery properties. 

Similarly, tandem hydroformylation/aldol sequences can be applied to the formation of bicyclic and spirocyclic compounds. Thus silyl enol ethers of 3-vinyl and 3-allyl cycloalkanones give ring anellated products (Scheme 33) [86,87]. 

Our study on the synthesis, structure and catalytic properties of rhodium and iridium dimeric and monomeric siloxide complexes has indicated that these complexes can be very useful as catalysts and precursors of catalysts of various reactions involving olefins, in particular hydrosilylation [9], silylative couphng [10], silyl carbonylation [11] and hydroformylation [12]. Especially, rhodium siloxide complexes appeared to be much more effective than the respective chloro complexes in the hydrosilylation of various olefins such as 1-hexene [9a], (poly)vinylsiloxanes [9b] and allyl alkyl ethers [9c]. 

It has also been proposed (DavyjGeneral Electric) to cause isobutene to react with allyl alcohol. The allyl r-butyl ether obtained is hydroformylated, hydrogenated and decomposed to butanediol and recyclable isobute ne ... 

Hydroformylation of the water-insoluble oleyl alcohol into formylstearyl alcohol has also been successfully achieved with a 96.6% yield by using a rhodium/trisul-fonated triphenylphosphine complex dissolved in an aqueous film supported on a high-surface-area silica gel (cf. Section 6.1) [13]. This supported catalyst has also been used to perform the hydroformylation of allyl 9-decenyl ether and 3-methyl-2-(2-pentenyl)-2-cyclopenten-l-one (as-jasmone). However, with the latter substrate, the aldehyde yields did not exceed 38% [14],... 

Miscellaneous.- A simple method to resolve racemic l,l -binaphthalene-2,2 -diol involves reaction with menthyl phosphorodichloridite (139) and separation of the diastereomeric phosphites by crystallisation from ether. The new cyclic chlorodiaminophosphine (140), prepared in and two new cyclic triaminophosphines (141) have been used to determine the enantiomeric purity of chiral alcohols, thiols, and amines by means of Ip n.m.r. New optically pure phosphites used for Rh catalysed asymmetric hydroformylation reactions are (142), two diastereomers of (143), and (144) the diphosphinite (145) was similarly employed. Some new cyclic aminophosphines (146) were prepared for use as ligands in asymmetric Pd catalysed allylic substitution reactions. 

Allylic alcohols are versatile substrates for hydroformylation. Hydroformylation of allyl alcohol typically favors the linear regioisomer, and this reaction formed the basis of a route to manufacture 1,4-butanediol [15]. Landis recently reported the use of a chiral diazaphospholane for the asymmetric hydroformylation of aUyl silyl ethers [16]. The TBDMS aUyl ether, formed from reaction of allyl alcohol with TBDMSCl, was hydroformylated in 96%ee and 2 1 branched/linear to give the Roche aldehyde (12) which is a widely used chiral building block. High molar substrate/catalyst ratios (10,000 1) and low syngas pressures (15 psi) make this reaction potentially attractive for commercial development. 

Very similar amounts of branched and linear aldehydes are obtained for aU the linear 1-alkenes (i.e. b l = 48/52 for 1-hexene at 20 C and 100 bar CO/H2, 1 1) [22], while an oxygen in b position to the vinyl group favors the formation of the branched isomers as observed for (allyl)ethyl ether (b l = 70/30) and similar substrates [lid]. It should be noted that the linear isomer largely predominate over the branched ones in the hydroformylation of 3-alkyl substituted allyl alkenes (i.e. 3-methylbut-l-ene) [5a]. 

As a special case, the formation of hemiacetals 2 (lactolization) during the hydroformylation of hydroxy-functionalized olefins, such as allyl or homoallyl alcohols, has to be mentioned (1, Y= O, Scheme 5.70). With these substrates, the reaction occurs in an intramolecular manner. In the presence of an external alcohol, the cyclic hemiacetal can further react to give a nonsymmetric cyclic acetal 3. Hemiacetals can be subjected to hydrogenation to afford diols 4. Under reducing conditions and in the presence of amines, amino alcohols 5 are formed both are valuable building blocks in fine chemistry. Alternatively, oxidation gives lactones 6 [5]. By dehydration of hemiacetals, cychc vinyl ethers 7 are formed. The same transformation with allylamines (Y=NR) gives cyclic hemiaminals, A/ ,0-acetals, lactames, or vinyl amines. 

A comparison between experimental and MO data on regioselectivity concerning the hydroformylation of several vinyl substrates (propene, 2-methylpropene, 1-hexene, 3,3-dimethylbutene, fluoroethene, 3,3,3-trifluoropropene, vinyl methyl ether, allyl methyl ether, styrene) with unmodified rhodium catalysts was reported. The activation energies for the alkyl rhodium intermediate formation, computed at either level along the pathways to branched or linear aldehydes, allowed one to predict the regioselectivity ratios. Steric effects may be less important for the unmodified carbonyl complexes and electronic factors dominate, assuming that alkene insertion in Rh-H is irreversible. 

The hydroformylation-allylation sequence was also used by Leighton for the synthesis of the aldehyde segment (Scheme 2.157). The formation of bis-allyl silyl ether 175... 

---