Primary alcohols rearrangement after

A related method was applied in the course of synthesis of a precursor of a macrolide antibiotic, protomycinolide IV. The migrating group was an a-trimethylsilylalkenyl group.68 In this procedure, the DiBAlH first reduces the ketone and then, after rearrangement, reduces the aldehyde to a primary alcohol. 

Selective protection of the primary alcohol gave 138 (P=TBDMS), which was then esterified with ( )-3-hexenoic acid to produce the key intermediate 139 for cyclization. Ireland ester-enolate Claisen rearrangement and hydrolysis produced a protected hydroxyacid, which, after reduction of the acid and deprotection of the alcohol, yielded meso diol 128 more quickly and efficiently than in the previous synthesis. The meso diol was then converted to the racemate of the lactol pheromone 130 as previously described. 

The strong aldehyde reaction of tin electrolyte, after the experiment was finished, indicates that the primary alcohol is partially oxidized further to propionic aldehyde, or that the propylene can yield propylene ox fie through the influence of the anodic oxygen, and, by molecular rearrangement, the a dehyde ... 

As previously stated, a distinct feature of this rearrangement is the retention of the anomeric information. This advantage is nicely illustrated by the direct synthesis of a carba-disaccharide from a disaccharide [65]. As shown in Scheme 8.35, maltose was first transformed into the thioglycoside 131. Manipulation to the free primary alcohol 132 was achieved using a classical sequence of reactions. At this point, glycosylation of methanol was realized in the presence of NCS to afford 133, and the unsaturated derivative 134 was obtained after iodination and elimination. Triisobutylaluminum induced rearrangement nicely afforded the carba-disaccharide precursor 135 in a yield of 89% as a mixture of two isomers. 

Lithium aluminum hydride reduction of c/s-l-hydroxybicyclo[4.2.0]octan-8-one gave the (la,6a,8/6)-bicyclo[4.2.0]octane-l,8-diol in 90% yield, exclusively. After treatment for a prolonged period (four days) at reflux in benzene containing a catalytic amount ofp-toluenesulfonic acid monohydrate, this trans-dio] had rearranged into cw-bicyclo[4.1.0]heptane-l-carbalde-hyde (16, 52%) which, on lithium aluminum hydride reduction, gave the corresponding primary alcohol, ds-l-hydroxymethylbicyclo[4.1.0]heptane (17). ... 

The proposed mechanism of the reaction is outlined in Scheme 1. Comparably with the described conversion 1— 2, after protonation of the alcohols 4b and 4c water is eliminated to form the carbenium ions 5b,c. As mentioned, 4a is reluctant to undergo the rearrangement. Obviously, under the conditions applied the elimination of water from the primary alcohol 4a fails and therefore the whole process cannot occur. Despite the delocalization of the positive charge in 5b,c and the enhanced stability of the carbenium ion, one trimethylsilyl group migrates from the central silicon atom to the neighboring carbon atom, generating the transient silylium ions 6b,c. Attack of the... 

In the presence of acid and a nucleophilic counterion, primary alcohols undergo Sn2 reactions. Secondary and tertiary alcohols tend to form carbocations in the presence of acid, capable of El and Srjl product formation, before and after rearrangement. 

In contrast, monofluoroallylic alcohol (S)-5 undergoes the Johnson-Claisen rearrangement in good yield after 7 hours at 130 C.33 The primary fluoride 6 is produced as the -isomer and with good 1,3-chiral transfer as the 7 -enantiomer. This ester is a key intermediate in the synthesis of 3 -fluoroapionuclcosides. 

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