Alcohols from conjugated carbonyls

Catalysts constituting a C2-symmetric 1,2-diamine have been used to hydrogenate a-aryl aldehydes to yield chiral alcohols, under dynamic kinetic resolution conditions. Hydrogenation of the carbonyl group of acylsilanes with 3 (presence of f-AmOK or NaBHr as activator) is apphcable to acquisition of a-silyl aUylc alcohols from conjugated acylsilanes. ... 

Conjugate carbonyl compounds contain centers of different hardness (hard Co and soft C=C), consequently hard hydrides favour conversion of enones to allylic alcohols [25]. Such a concept could be operative also in our case since C=C bond is preferably reduced on going from Mgo to SrO. 

This is quite different to the reactivity of a C=C double bond conjugated with a carbonyl group, which, as you have just seen, reacts with nucleophiles such as cyanide, amines, and alcohols. The conjugated system is different from the sum of the isolated parts, with the C=0 group profoundly affecting the reactivi- true electJ on distribution lies somewhere ty of the C=C double bond. To show why, we can use... 

We need carbonyl groups to do conjugate addition so the tertiary alcohols will have to be made from them. In Chapter 9 (p. 222) we saw how to make such tertiary alcohols from esters and organometallic compounds and in Problem 1 of this set we saw how to do double conjugate additions on unsaturated esters - all the pieces fit together. 

Alternatively, 2-(chloromethyl)-3-iodo-l-propene reacted with aldehydes or ketones to give after basic treatment methylenetetrahydrofuran in excellent yields. The reaction is as expected chemo- and regioselective conjugated carbonyl compounds gave 1,2-addition, and aldehydes react more preferably than ketones [106]. Simharly, 3-chloro-homoallylic alcohols were prepared in high yields from the reaction of 2,3-dichloropropene with carbonyl compounds in a two-phase system containing a small amount of acetic acid. In this reaction, the presence of water in the reaction medium was shown to be essential as the reaction did not occur under non-aqueous conditions [107]. 

Sequential Heck reaction and hydrosilylation of carbonyl have been carried out with the Grubbs I catalyst. AUyUc alcohols can be S3mthesized via conjugated carbonyl compounds prepared from cross-metathesis in situ by reduction with j-Bu2AlH. An access to enantiomeric 2,3-dihydroxyalkanoic esters is based on cross-metathesis, dihydroxylation and methanolysis. ... 

More recently, using the cyclometallated iridium C,(7-benzoate derived from allyl acetate, 4-methoxy-3-nitrobenzoic acid and BIPHEP, catalytic carbonyl crotylation employing 1,3-butadiene from the aldehyde, or alcohol oxidation was achieved under transfer hydrogenation conditions [274]. Carbonyl addition occurs with roughly equal facility from the alcohol or aldehyde oxidation level. However, products are obtained as diastereomeric mixtures. Stereoselective variants of these processes are under development. It should be noted that under the conditions of ruthenium-catalyzed transfer hydrogenation, conjugated dienes, including butadiene, couple to alcohols or aldehydes to provide either products of carbonyl crotylation or p,y-enones (Scheme 16) [275, 276]. 

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