Stereoselectivity hydrogenolysis

Highly regio- and stereoselective 4a-deuteration in steroids is possible by the hydrogenolysis of the cyclic allylic /3-carbonate 628 with NaBD4. the extent of 6a-deuteration is only 3%[393],... 

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. 

Addition of a hydroxy group to alkynes to form enol ethers is possible with Pd(II). Enol ether formation and its hydrolysis mean the hydration of alkynes to ketones. The 5-hydroxyalkyne 249 was converted into the cyclic enol ether 250[124], Stereoselective enol ether formation was applied to the synthesis of prostacyclin[131]. Treatment of the 4-alkynol 251 with a stoichiometric amount of PdCl2, followed by hydrogenolysis with formic acid, gives the cyclic enol ether 253. Alkoxypalladation to give 252 is trans addition, because the Z E ratio of the alkene 253 was 33 1. 

Pd(0)-catalyzed hydrogenolysis of vinylepoxides offers an attractive regio- and dia-stereoselective route to homoallylic alcohols (Scheme 9.36) [104, 155, 156]. Thus, hydrogenolysis of ( ) olefin 88 affords syn isomer 89 with inversion of configuration at the allylic carbon, while subjection of (Z) isomer 90 to identical reaction conditions results in the anti isomer 91. The outcomes of these reactions are ex-... 

Addition of organometallics to hydrazones provides hydrazines1, which can be converted to the corresponding amines by hydrogenolysis. Hydrazones can therefore be regarded as masked imine derivatives of ammonia. This methodology has been utilized successfully for numerous stereoselective syntheses of amines and amine derivatives2-23. 

Vinyl ethers and vinyl esters are not employed extensively in organic transformations. During the synthesis of phlegmarine, however, the stereogenic center at C-10 was to be introduced stereoselectively by catalytic hydrogenation-hydrogenolysis of the vinyl triflate (Scheme 4.7). 

Optically active 2-oxazolidinones and 2-thiazolidinones are versatile compounds as chiral auxiliaries. 5a b (4R,5S)-4,5-Diphenyl-2-oxazolidinone has been used for the synthesis of optically active amines6 because of its high stereoselectivity and easy deprotection by hydrogenolysis after the reaction. Compared with several preparations73-0 of (4R,5S)-4,5-diphenyl-2-oxazolidinone reported so far, this method,... 

Hydrogenolysis of the benzylether of lactone 141 (H2, 10% Pd/C) quantitatively afforded (-)-wikstromol ent-3). The overall yield of ent-3 from diisopropyl malate 107 over six steps was 30% [62]. This strategy for the construction of optically-active lactone lignans provided a short and stereoselective synthesis with comparably good overall yield. 

Improved synthesis by this method has been achieved in order to obtain solenopsin A (Id) more stereoselectively 388). A cis and trans mixture of pyridine derivative 158, obtained from 156 by the Wittig reaction, was reduced by Raney nickel catalyst in the presence of PtOj to yield the m-piperidine (Ic). The Af-nitroso derivative 159, obtained from Ic by treatment with isoamyl nitrite, was treated with potassium rert-butoxide and then subjected to hydrogenolysis over Raney nickel to give a mixture of ( )-solenopsin A (Id, 1 part) and its isomer (Ic, 1 part) (Scheme 3). 

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