Spontaneous ring enlargement during the free-radical bromination of 2-benzyl-1,3,3-trimethyl- and 2-benzyl-3,3-dimethylbicyclo[2.2.1]heptan-2-ol

Abstract

Notes that of the betaine 5,9 and thus the former give stable y lides and the latter gives a betaine.Possibly the high acidity of the betaine in the case of the ylide lb is due to a resonance effect of the phenyl group. Experimental SectionMaterials.-Benzoyl isocyanate was prepared according to the procedure of Speziale:10 bp 99-101°( 20 mm); ir 2240 cm-1 (NCO).The ylides la,11 4a,12 and 4b12 were prepared according to the known procedures. The physical properties were identical with reported data. Reaction of the Ylide la.-Benzoyl isocyanate (0.02 mol) dissolved in 3 ml of benzene was added dropwise to 0.02 mol of the ylide la dissolved in 200 ml of benzene under a nitrogen stream. The mixture was stirred at 50°for 3 hr. The resulting precipitate was filtered off and recrystallized with methanol to give 6.0 g (93%) of the ylide 2a:

Synthesis of Functionalized Bicyclo[3.2.1]octanes and Their Multiple Uses in Organic Chemistry

“…271 Finally, the cornerstone transformation in a total synthesis of cedranediol is the regiospecific ring enlargement of tricyclic olefin 473 to give the properly functionalized carbon framework 474. 272 The 1,2-rearrangement of halohydrins introduced by Sisti, 273 was recently included in a synthetic strategy directed toward the synthesis of glycinoeclepin A from monoprotected bicyclooctanedione 476, easily obtained in 50% yield by transposition of hydroxy dibromide 475. 274 Similarly, pinacol-type fragmentation of tricyclic mesylate 477 furnished the expected rearranged carbon skeleton 478, involved in the total synthesis of various zizane sesquiterpenes.…”

General and Efficient Insertions of Carbons Carrying Aryl and Heteroaryl Groups: Synthesis of α-Aryl- and α-Heteroaryl-Substituted Ketones

“…Carbon insertion is the most straightforward and most commonly used strategy for this purpose. The numerous procedures for the insertions of carbons bearing C-linked substituents into aldehydes and ketones available in the literature can be classified into the following categories: (i) diazo insertion reactions utilizing ethyl diazoacetate, − α-diazo ketones and aldehydes, diazoalkanes, and aryl diazomethanes; , (ii) β-oxido carbenoid chemistry as initiated by Yamamoto using dihalomethyllithiums and recently extensively developed by Yamakawa 1 with chloromethyl sulfoxides as advantageous reagents for the insertions of carbons bearing an alkyl 1c,13 and an aryl 13 groups into aldehydes and ketones; (iii) semipinacol-type rearrangements, alkylidene insertions utilizing α-lithioalkyl sulfoxides and selenoxides − and arylmethylene insertions via the rearrangement of halohydrins, derived from the addition of benzylmagnesium chloride to carbonyl compounds, followed by α-bromination; and (iv) other approaches include ring expansions of cyclic ketones via radical processes − and more complex pathways …”

New ring expansion procedure. VI. Decomposition of the magnesium salts of some 1-(.alpha.-bromobenzyl)-1-cycloalkanols and bicycloalkanols

“…2-Methyl-l-(a-bromobenzyl)-l-cyclopentanol (12) was prepared as described for 2 (0.100 mol of 13 employed). After removal of the solvent a light yellow oil remained: ir 3500 cm™1; nmr r 4.80 [s, -C(H)(Br)(Ph)].…”