Benzoyl migration

Dibenzoyldiaziridine (130) thermally rearranges with ring opening and benzoyl migration to the dibenzoylhydrazone (138) (67CB142). 

The tetramethyl ether (15) mentioned above was also converted to its equatorial monobenzoate (16), and the latter methylated and de-esterified to give a hexol pentamethyl ether. As benzoyl migration occurred during methylation, this pentamethyl ether had the configuration 18, and was not the diastereomer (19) mentioned above (27). 

In early experiments, the pentamethyl ether (18) was treated with phosphorus pentachloride in the hope of obtaining a chloropentol reducible to ( — )-proto-quercitol. (Allowing for the benzoyl migration, the expected product would have been (— )-uibo-quercitol (11).) Surprisingly, the quercitol actually obtained after demethylation and dehalogena-tion was neither of these but still another previously known isomer, meso-scyllo-quercitol (24) (27). 

Ethanolysis of 2,4-di-0-benzoyl-3,6-dideoxy-L-ara mo-hexono-l,5-lactone (92) afforded ethyl 2,4-di-0-benzoyl-3,6-dideoxy-L-araW/to-hexonate (93a). On being kept, compound 93a was slowly converted into 2,5-di-O-benzoyl-3,6-dideoxy-L-ara6mo-hexono- 1,4-lactone (94). This transformation involves O-4 — 0-5 benzoyl migration, with formation of ethyl 2,5-di-0-benzoyl-3,6-dideoxy-L-araA ohexonate (93b) as an intermediate (89). 

These compounds are used for the preparation (EtsN, MeCN) of the corresponding ylides 182. These y tides with DM AD give 183 and 184 ( /Z mixture). Compound 183 seems to be formed by a new type of intramolecular benzoyl migration of an intermediate 1 1 adduct. 

Finally, in the case of compound 17, the system was transformed to the sialic acid glycoside 20. The key step in this regard was the benzoyl migration... 

It has long been known that under the influence of mineral acid fraax-benzalacetophenono oxide (JmiM-chaloone oxide) uiidminr< rearrangement to an aldehyde.1881 To determine whether phenyl or benzoyl migration attends this isomerization, House816 subjected labeled frons-benzalacetophenone oxide to the action of boron ui-fluoride, and examined isotopic distribution in the product. Incorporation of 98% of the 14C label into the aldehyde carbon (Eq. 477) c-Jrai ly established that benzoyl migration is involved. 

There exists an appreciable tendency for aldehyde formation by 1,2-hydride shift, however, when a terminal epoxide is involved. With aorylophenone oxide, for example. House and Wasson4 demons rnti il isotopkally that benzoyl migration and 1,2-hydride transfer occur to a comparable extent (Eq. 481). 

Brigl and Muhlschlegel148 were able to isolate 3,4,5,6-tetra-O-benzoyl-D-glucose diethyl thioacetal from the thioacetal and benzoyl chloride in an aqueous solution of alkali. When the reaction is carried out in pyridine, both the tetra- and the penta-benzoate are obtained. The tetrabenzoate has been described as a convenient intermediate for the synthesis of 2-0-methyl-n-glucose and its derivatives.149 It is somewhat surprising that position 2 should exhibit this resistance to benzoylation, since preferential methylation occurs in this position. A benzoyl migration could possibly explain the anomalous observations. 

Attempted sodium hydride mediated benzylation of methyl 3-0-benzoyl-4,6-0-benzylidene-P-D-galactopyranoside failed due to a benzoyl migration [65]. The acyl group migration and removal are also responsible for only 62 % yield of benzyl 2-acetamido-3,6-di-0-acetyl-4-0-benzyl-2-deoxy-a-D-glucopyranoside. Thallium eth-oxide instead of sodium hydride or alkoxide successfully restrained the acetyl group migration in this reaction [35]. 

Pyridine catalyses the reaction of 1,2-diaryldiones with DMAD to give diaroyl maleates in a rearrangement that involves a benzoyl migration and occurs with complete stereoselectivity (Scheme 76).113 A mechanism has been proposed. 

In the carbohydrate series, acetates can be cleaved selectively in the presence of benzoates [Scheme 4.329] and p-bromobcnzoates using p-toluenesulfonic acid monohydrate (1 equivalent per acetate) in dichloromethane-methanol (9 1) at 4 °C in 7 h or room temperature in 24 h.616 No benzoyl migration is observed. The method also works in comparable yield with camphorsulfonic acid although the reaction takes 2 days at 40 °C and 3 days at room temperature. 

The l-aza-S-oxa-di-iT-methane rearrangement of (25) does not occur. Instead, cis-trans isomerization and photoelimination of methanol are observed for this oxime (equation 21) Finally, the l-oxa-4-aza-di-iT-methane rearrangement of compound (26) also did not take place. This substrate gave rise to the photo-induced 1,5-benzoyl migration shown in equation (28). ... 

An analogous acyl group transfer has been observed in acylated hydrazones of 3-hydroxybenzo [ b] thiophene-2-carboxaldehyde and 1,3-benzoyl migration and E-isomerization pathways compete on irradiation of certain 4-acyloxy-2-azabuta-1,3-dienes, the... 

Rearrangements. o-Benzoyloxyacetophenone undergoes benzoyl migration to give o-hydroxydibenzoylmethane when a solution in pyridine is treated with 7 g. 

Details of the photochemical behaviour of the p, - unsaturated enones (186) has been reported. This supplements the report made earlier in note form. The reaction described involves the photoconversion of the enones (186) into the imines (187) and (188) by a path which is thought to involve a 1,5-benzoyl migration. The terminus for this is a pendant phenyl group. Such a process has not previously been described. An... 

DABCO, ethanol, pyridine, 20-70°C, >94% yield. This method is faster than the thiourea method by a factor of about 9. It does not cause benzoyl migration in the carbohydrates examined. ... 

Hassner and his co-workers69 have reported an example of 1,3-benzoyl migration in the rearrangement of the triene (120) to (121). 

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