Carbonyl compounds homoallylation, 1,3-Dienes

Keywords Allylation Carbonyl compound Dienes Homoallylation Nickel catalysis Reductive coupling... 

Nickel-Catalyzed Reductive Homoallylation of Carbonyl Compounds with 1,3-Dienes... 

The mode of reaction of titanacydobutenes with carbonyl compounds is largely dependent on steric factors (Scheme 14.31) [72]. Ketones and aldehydes tend to insert into the titanium—alkyl bond of 2,3-diphenyltitanacydobutene, and homoallylic alcohols 70 are obtained by hydrolysis of the adducts 71 [65a,73]. On the contrary, when dialkyl-substi-tuted titanacydobutenes are employed, the reaction with aldehydes preferentially proceeds through insertion into the titanium—vinyl bond. Thermal decomposition of the adducts 72 affords conjugated dienes 73 with E-stereoselectivity as a result of a concerted retro [4+2] cycloaddition [72]. 

Tamaru and Kimura have recently developed a three-component coupling reaction of carbonyl compounds, 1,3-dienes, and dimethylzinc leading to homoallylic alcohols 30 via Ni-catalyzed conjugate addition of the carbonyl compound to the 1,3-diene in a 1,4-fashion (Scheme 8.11) [44], They later showed that 1,3-dienes... 

The reaction of 1,3-dibromopropene with carbonyl compounds mediated by indium in water gives 3,3-disubsti-tuted propene 63 (Scheme 55). In the formation of 63, 1,3-dibromopropene acts as a w-allyl dianion synthon. Aromatic aldehydes generally have a higher selectivity than aliphatic ones in the product formation. Unsubstituted and electron-withdrawing group-substituted benzaldehydes give mainly 3,3-disubstituted propene 63. For electron-rich benzaldehydes, the formation of both 3,3- 63 and 1,3-disubstituted propene 64 is dramatically decreased and the selectivity is reversed completely to give diene 65 and homoallylic alcohol 66.219... 

Carbonyl compound alkylations. Allylic alcohols and homoallylic silyl ethers are prepared from alkynes and dienes, respectively. 

Allenic alcohols.3 The reaction of allylsilanes with carbonyl compounds catalyzed by this salt to give homoallylic alcohols (9, 455-446) has been extended to a synthesis of a-allenic alcohols. Use of TiCl4 as catalyst results in a 2-chloro-l,3-diene. 

Homoallylation. Carbonyl compounds afford 4-aIkenols from a Ni-catalyzed condensation with 1,3-dienes that is promoted by diaUcylzinc (as alternative to the previously reported triethylborane). With diethylzinc there is an overall reductive alkylation but dimethylzinc also donates a methyl group to the product. ... 

Allyl complexes have contributed significantly to the development of the organometallic chemistry of nickel and the applications of nickel complexes in organic synthesis, for example, nucleophilic attack on coordinated allyl ligands. In addition, allylnickel complexes have been identified as key intermediates in the oligomerization and cyclization of olefins and dienes. For example, the Ni(0)-catalyzed hydrocyanation of butadiene to adiponitrile, the main component of a major commercial process for the production of nylon, involves Ni (7r-allyl) intermediates. Moreover, the 77-rearrangements of allylnickel species have helped explain the facile isomerization of olefins in the presence of nickel complexes. The Ni-catalyzed homoallylation of carbonyl compounds with 1,3-dienes also involves Ni(7r-allyl) complexes this subject has been reviewed recently. New applications include the cleavage of G-G bonds in the deallylation of malonates, the preparation of cyclopentenones by carbonylative cycloaddi-... 

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