Benzyloxy compounds, rearrangement

All nuclear nucleophilic substitutions on derivatives of compound 4 have involved the replacement of a substituent at position 7 (the equivalent of the y -position in pyridine). In the 7-chloro derivative 244, replacement is possible by methoxide ion,151 by ammonia (with some rearrangement)192 and by amines,151 and by thiourea to give the sulfide (245).151 Substituted 7-chloro derivatives undergo replacement by benzyl oxide ion to give a 7-benzyloxy derivative155,220 and by azide,153 hydrazine,216 hydrosulfide (to give the 7-thione166), and methyl thiolate.220 Some of these compounds carry D-ribofuranosyl benzoate substituents on N-2 or N-3, and methoxide ion... 

Whereas the lithium enolates of acetate and propionate esters of difluoroallylic alcohols are known to fragment rapidly, methoxy- and benzyloxy-acetates have been found151 to form chelated enolates which undergo a smooth [3,3]-sigmatropic rearrangement as their silyl ketene acetals to afford highly functionalized difluoro compounds (see Scheme 33). Allenic silyl ketene acetals (117) have been used152 to prepare 2-substituted methyl 3,4-dienoates (118). 

Allyloxy derivatives from pyridine-1-oxides posed still a further element of uncertainty. This arose from the facile isomerization of 2-alkoxypyridine-l-oxides into the corresponding l-aIkoxy-2-pyri-dones even under the conditions of synthesis. Thus, treatment of 2-chloropyridine-l-oxide with sodium allylalcoholate afforded the 2-allyloxypyridine-l-oxide whereas treatment of the same starting compound with sodium benzyloxide gave l-benzyloxy-2-pyridone. A closer investigation revealed that 2-benzyloxypyridine-l-oxide rearranged readily under the experimental conditions of synthesis.6... 

Hydrolysis of 3/8-benzyloxy-14a,15a-epoxy-5a-cholest-7-ene with aqueous KOH-EtOH gave the rearranged triol (16) which with HCl-EtOH gave the enone (17). Treatment of 5a,10a-epoxy-A " -steroids with lithium organo-cuprates gave 11/3-substituted 5a-hydroxy-A -compounds and is exemplified by... 

By treating o-chloromethylaniline hydrochloride with cu-benzyloxy-butyro- and -valeronitriles in refluxing o-dichlorobenzene in the presence of stannic chloride, Mufloz and Madroilero obtained the tricyclic compounds 124 and 202, respectively. The pyrido[2,l- )]quinazolines 289 were prepared by refluxing o-chloromethylaniline hydrochloride in dichlorobenzene with 2-chloropyridine and its tetrahydro derivative. The latter was obtained in situhy Beckmann rearrangement of cyclopentanone oxime with phosphorus pentachloride. 

Most examples of [1,2]-Wittig rearrangements involve relatively basic carbanions. However, a few reports have demonstrated that enolates derived from a-alkoxy carbonyl compounds can also participate in [1,2]-Wittig rearrangements. For example, a-benzyloxy lactam 34 was converted to 35 in 63% yield upon treatment with LiHMDS. Related enolate Wittig rearrangements have also been used in tandem processes as described below. 

---