Crotyl anions, reactions

C, complex 185 isomerizes to the (a fi-allyl)Fe(CO)3" anion (186), which may be trapped by reaction with Me3SnCl to give the corresponding ( nt/-crotyl)Fe(CO)3SnMe3 complex (187). Isomerization of 187 to the thermodynamically more stable (svn-crotyl) isomer (188) occurs only at a higher temperature (55 °C). 

In the first step, reagent 7, developed by Hoffmann, is used lor asymmetric crotylation in order selectively to create the stereogcnic centers at C-10 and C-ll (dr >98 2).13 14 This produces compound 24, which is subsequently protected at C-11 as the p-mclh-oxyben/yl ether Protection is accomplished by reaction of the anion of the alcohol with commercially available p-methoxyben/yl chloride.15 16... 

Diene)Mn(CO)3 anions are stable in solution, and have been characterized by infrared and NMR spectroscopy. However, exposure of the anion solution to oxygen results in decomposition to give the free ligand. Reduction of (crotyl)Mn(CO)4 (62) gives the manganese-carbonyl transfer reagent ( -2-butene)Mn(CO)4. Reaction of 1,3-cycloheptadiene, 1,3-cyclooctadiene, 1,3,5-cycloheptatriene or 1,3,5,7-cyclooctatetraene... 

Finally, Maikov and coworkers used terpene-derived IV,IV -dioxide 21.22 in a total synthesis of marine serrulatane diterpene (—)-elisabethadione 21.67 (Scheme 21.9) exhibiting potent anti-inflammatory activity. Asymmetric crotylation of cinnamaldehyde 21.65 on a 5 mmol scale afforded syn-homoallylic alcohol 21.66 in 82% yield, 94% enantiomeric excess and with complete distereoselectivity. Other key reactions to install the stereogenic centres of the target molecule included anionic ory-Cope rearrangement and cationic cyclisation. ... 

Benzylideneacetone)Fe(CO)3 may be reduced stepwise electrochemically to yield a radical anion and dianion, respectively. Reaction of the former with crotyl bromide yields ( -l-methylallyl)2Fe(CO)2. (Benzylideneacetone)Fe-(CO)aPPh3 has been prepared, and acts as a useful source of the Fe(CO)2PPh3 moiety in the preparation of (diene)Fe(CO)2PPh3 complexes. A kinetic study of the reaction between chpt and several (a/S-unsaturated ketone)Fe(CO>3 complexes to yield (chpt)Fe(CO)s reveals a stepwise displacement containing both associative and dissociative pathways. ... 

Allyltrimethylsilanes can be activated by a nucleophilic Lewis base such as TBAF and metal alkoxides to undergo carbonyl allylation. The reaction of crotylsilane gives a regioisomeric mixture of carbonyl addition products, suggesting that free allylic anion is possibly involved (Scheme 3-116). On the other hand, the reaction of crotyl(trifluoro)silane shows perfect ) selectivity derived probably Irom a six-... 

The titanium- ate complexes of a-methoxy allylic phosphine oxides, generated in situ by reaction of the corresponding lithium anion and Ti(0-i-Pr)4, condense with aldehydes exclusively at the a-position to produce homoallylic alcohols in a diastereose-lective fashion. The overall result is the three-carbon homologation of the original aldehyde, and this protocol has been used in a synthesis of (-)-aplysin-20 from nerolidol. The titanium- ate complex produced by reaction of the chiral lithium anion of an ( )-crotyl carbamate with Ti(0- -Pr)4 affords -y-condensation products (homoaldols) on reaction with aldehydes. Allyl anions produced by the reductive metalation of allyl phenyl sulfides condense with a,p-unsaturated aldehydes in a 1,2-manner at the more substituted (a) allyl terminus in the presence of Ti(0-i-Pr)4. 1,2-Addition of dialky Izincs to a,p-unsaturated aldehydes can be achieved with useful levels of enantiocontrol when the reaction is conducted using a chiral titanium(IV) catalyst in the presence of Ti(0- -Pr)4 (eq 20). Higher ee values are observed when an a-substituent (e.g. bromine) is attached to the substrate aldehyde, but a -substituent cis-related to the carbonyl group has the opposite effect. 

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