Allyl carbinol

Allylic boranes such as 9-allyl-9-BBN react with aldehydes and ketones to give allylic carbinols. The reaction begins by Lewis acid-base coordination at the carbonyl oxygen, which both increases the electrophilicity of the carbonyl group and weakens the C-B bond to the allyl group. The dipolar adduct then reacts through a cyclic TS. Bond formation takes place at the 7-carbon of the allyl group and the double bond shifts.36 After the reaction is complete, the carbinol product is liberated from the borinate ester by displacement with ethanolamine. Yields for a series of aldehydes and ketones were usually above 90% for 9-allyl-9-BBN. 

Scheme 9.3 illustrates some examples of syntheses of allylic carbinols via allylic boranes and boronate esters. Entries 1 and 2 are among the early examples that... 

Related catalytic enantioselective processes It is worthy of note that the powerful Ti-catalyzed asymmetric epoxidation procedure of Sharpless [27] is often used in the preparation of optically pure acyclic allylic alcohols through the catalytic kinetic resolution of easily accessible racemic mixtures [28]. When the catalytic epoxidation is applied to cyclic allylic substrates, reaction rates are retarded and lower levels of enantioselectivity are observed. Ru-catalyzed asymmetric hydrogenation has been employed by Noyori to effect the resolution of five- and six-membered allylic carbinols [29] in this instance, as with the Ti-catalyzed procedure, the presence of an unprotected hydroxyl function is required. Perhaps the most efficient general procedure for the enantioselective synthesis of this class of cyclic allylic ethers is that recently developed by Trost and co-workers, involving Pd-catalyzed asymmetric additions of alkoxides to allylic esters [30]. 

Nucleophilic Addition by Allylboron Derivatives. Allylboranes such as 9-allyl-9-BBN react with aldehydes and ketones to give allylic carbinols. Bond formation takes place at the y carbon of the allyl group, and the double bond shifts.33... 

The reaction of allylic Grignard reagents with aldehydes to produce allylic carbinols does not always proceed smoothly. In the reaction of 3,4-methylene dioxybenzaldehyde with allyl alcohol (1.5-3.0 moles) at ambient temperature... 

This boast was somewhat premature, because the most difficult step of the four-step process was still unsolved. The dehydration of butylene glycol to the desired butadiene, as Meisenburg had remarked eleven years earlier, presented great difficulties, because apart from butadiene, other products of the dehydration were also formed, which gave rise to heavy contamination. I.G. Hochst had developed an alum catalyst, based on earlier work at Bayer, but Richard Leopold of Hochst ruefully reported in April 1927 that one of the hydroxyl groups resisted dehydration, giving rise to allyl carbinol and crotyl alcohol as by-products. ... 

It was also found that the in situ generation of allylic organolithium compounds (this method avoids the necessity of synthesizing an allylic halide) in this manner can be used to produce allylic carbinols when aldehydes and ketones were present in the reaction mixture as electrophiles. 

Phenyl-[a-methylamino.y-phenyl-allyl]-carbinol IS 1288 vgl. a. 27 1 234. o>.(2.4.5- Priniefiiyl-anilino].aoetophenon 14 1371. 

Suitable catalysts for ring closure reactions are cobalt carbonyls [123, 280, 673, 674], rhodium carbonyls [280, 678], iron carbonyl [123] and certain palladium compounds [679]. Nickel carbonyls, the active catalysts in the Reppe syntheses, are inactive in most cases [123, 673]. A few examples in which nickel is active are the formation of phenols from allyl halides, acetylene and carbon monoxide, which is only a side reaction, and the mechanistically unclear formation of lactones from allyl carbinol and bu-tyne-l-ol-4 [438]. 

Another example is the carbonylation of allyl carbinol under the conditions of the Reppe reaction [525], yielding a-methyl-y-butyrolactone plus S-valerolactone. 

Starting from the petrochemicals acetylene and acetone, allylic carbinol is obtained by partial hydrogenation of the triple bond and brominated in the next step to TM 2.13a. 

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