Regioselectivity hydrogenolysis, formate reactions

An interesting catalyst behaviour has been observed in the hydroformylation of alkenes here, the iridium complex (135) first activates hydrogen via the hydrogenolysis of the Ir-O bond upon the formation of (136), which then reacts with the alkene and CO to produce MeCH2CH=0. Notable is the participation of the side arm of the ligand and no change of the oxidation state of the metal. However, the regioselectivity of the reaction (branched/linear) is rather poor (Scheme 9). ... 

The Pd-catalyzed hydrogenolysis of vinyloxiranes with formate affords homoallyl alcohols, rather than allylic alcohols regioselectively. The reaction is stereospecific and proceeds by inversion of the stereochemistry of the C—O bond[394,395]. The stereochemistry of the products is controlled by the geometry of the alkene group in vinyloxiranes. The stereoselective formation of stereoisomers of the syn hydroxy group in 630 and the ami in 632 from the ( )-epoxide 629 and the (Z)-epoxide 631 respectively is an example. 

The final example in this section is classed as a 1,3-dipolar addition, as this is the key step in the reaction, although actual formation of the pyrrolizidine ring is by an intramolecular alkylation process. Tufariello and Tette showed that A -pyrroline-N-oxide added regioselectively in a 1,3-dipolar fashion to the dipolarophile to give an isoxazolidine (95) in 80% yield [Eq. (27)]. The pyrrolizidine ring was then formed by hydrogenolysis of the methanesulfonate derivative of 95 in 95% yield. The dehydration and reduction steps were not so efficient, and a mixture of reduction products was obtained. Half of this mixture was ( )-supinidine (96) and the remainder consisted of fully reduced isomeric 1-hydroxymethylpyrrolizidines. 

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