Isopropyl group transfer

Table I. BFg-Catalyzed Isopropyl Group Transfer to Phenol (12)...

The data on isopropyl group transfer in Table I show that the secondary aliphatic-aromatic carbon-carbon bond is very reactive when the aliphatic group is linked to either a phenolic ring or a phenanthrene ring. The reaction is very slow when the isopropyl group is linked to a nonactivated benzene ring. The relative reactivities of the secondary carbon bond in the first two structures could not be evaluated because the isopropyl group transfer went to completion in the case of o-iso-... 

Oxaziranes derived from isobutyraldehyde react with ferrous salts to give only substituted formamides fEq. (23)], The chain propagating radical 30 thus suffers fission with elimination of the isopropyl group. An H-transfer would lead to substituted butyramides, which are not found. Here is seen a parallel to the fragmentation of alkoxyl radicals, where the elimination of an alkyl group is also favored over hydrogen. The formulation of the oxazirane fission by a radical mechanism is thus supported. 

The aldehyde or ketone, when treated with aluminum triisopropoxide in isopropanol as solvent, reacts via a six-membered cyclic transition state 4. The aluminum center of the Lewis-acidic reagent coordinates to the carbonyl oxygen, enhancing the polar character of the carbonyl group, and thus facilitating the hydride transfer from the isopropyl group to the carbonyl carbon center. The intermediate mixed aluminum alkoxide 5 presumably reacts with the solvent isopropanol to yield the product alcohol 3 and regenerated aluminum triisopropoxide 2 the latter thus acts as a catalyst in the overall process ... 

The isopropyl group discourages P-H transfer, leading to the exclusive formation of Al-PEs. The Al-PEs can be readily transformed to a variety of functionalized PEs and to PE-based and polar polymer-based block and graft copolymers, using established methods. The selective synthesis of vinyl- and Al-terminated PEs with Zr-FI catalysts shows the critical importance of the substituent on the imine-N for polymerization catalysis. 

This means that the isopropyl group stabilises the secondary ion sufficiently (compared to but-l-ene) for hydride transfer reactions to be suppressed, at least at low temperature. At about -120 °C a high polymer of structure (IV) is formed. This is a true phantom polymer, since there exists no corresponding monomer. Evidently, at the very low temperature the propagation reaction which would lead to structure (III) becomes much slower than the isomerization reaction ... 

Fig. U.4 Reaction sequence showing how a small e.e. of the reagent is converted to a large e.e. of the product by a metal-assisted reaction. In the case shown, a 1 % e.e. of L-valine produced a 51 % e.e. of L-pyrimidine alcohol by the reductive asymmetric transfer of an isopropyl group from zinc to the carbonyl carbon of the...

The mechanism of p-lactam formation is thought to involve photoinduced electron transfer from nitrogen to the benzoyl group followed by transfer of a tertiary y-proton from one of the isopropyl groups to the carbonyl oxygen... 

A RhCp complex (S,S)-6 (Cp =pentamethylcyclopentadienyl), which is iso-lobal with Ru(rj6-arene) complex (S,S)-5 (Scheme 13), effected the transfer hydrogenation of a cyclic imine substituted by an isopropyl group with an S/C of 200 in the presence of a 5 2 mixture of formic acid and triethylamine to give the R amine in 99% ee (Scheme 13) [31]. When the reaction was performed with an S/C of 1,000, the optical yield decreased to 93%. The methyl imine was reduced with a 91% optical yield. Reduction of a cyclic sulfonimide resulted in the R sul-tam in 81% ee. 

A mixture of (35,45)-[4— H]-mevalonate and (3/ ,4/ )-[4— H]-mevalonate and ( )-[2— C]-mevalonate [( )-463 ] was fed to whole plants of C. japonica by the cotton-wick method (Scheme 62). The ratio of to T of the labelled tutin (11 ) showed that one of the three tritium atoms survived the biosynthetic pathway, with the other two tritium atoms lost to oxidation. For the tritium at position C(4) it is only possible for it to remain if the hydrogen transfer occurs in a one-step reaction. In the case of a double 1,2-hydrogen transfer, the tritium atom would be incorporated in the isopropyl group and vanish with the dehydrogenation to the... 

The diastereomerically pure thiazolium salt 509 which bears a 2-/i t7-butylphenyl substituent at the nitrogen atom was converted into a mixture of 510 and its atropisomer 510 (dr = 75 25) upon treatment with base (Scheme 128). The stereogenic center in the intermediate carbene favors one rotamer 510. Upon reaction with benzaldehyde, it accounts in a similar fashion for the formation of the major enol diastereoisomer 511 over 511, which, in turn, leads to the major enantiomer 512 rather than 512 observed in the benzoin condensation catalyzed by 509. The concept of axial chirality was proven to be viable for an efficient chirality transfer. Replacement of the isopropyl group at C-4 by the bulkier 2-phenyl-2-propyl substituent using 8-phenylmenthone is likely thought to increase the ee <2004EJ02025>. 

Extraannular chirality transfer has been observed for alkylations of acyclic ketone enolates having chiral (3-carbon atoms (Scheme 24). In these reactions, methylation occurs anti to the (3-dimethylphe-nylsilyl and (3-isopropyl groups with good to excellent diastereoselectivity. Variation in the size of the... 

The Q-Max process typically produces nearequilibrium levels of cumene (between 85 and 95 mol%) and DIPB (between 5 and 15mol%). The DIPB is fractionated from the cumene and reacted with recycle benzene at transalkylation conditions to produce additional cumene. The transalkylation reaction is believed to occur by the acid catalyzed transfer of one isopropyl group from DIPB to a benzene molecule to form two molecules of cumene, as shown in Fig. 5... 

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