Favorskii rearrangement of 1-bromo-7,7-dimethylnorbornanone

Camphor: a chiral starting material in natural product synthesis

“…According to the mechanistic proposals that are shown in Scheme 4, the presence of an endo-bromo-substituent at C-3 in camphor ensures that C(9)-sulp hona tion and C(9)-bromination provides 3,9-disubstituted derivatives with retention of configuration. However, it seems reasonable to suggest that other endo-substituents at C-3 would produce a similar result [the assumptions being (a) that the reactivity of the camphor derivative is not drastically reduced by the substituent and (b) that the 3-end0 configuration is stable under the reaction conditions : for example, 3-endo-bromocamphor is much more readily brominated than camphor and is also much more stable than its 3-exo-isomer]; consistent with this proposal is the observation that bromination (by Br2 and C1SO3H, for 48 hours) of 3-endo-methylcamphor (33) (Scheme 4) provides (+ )-9-bromo-3-endo-methylcamphor (34) in 50% yield.5 3-endo-Methylcamphor (33) is prepared by methylation (by LiNPrj and MeI, at 0 "C) of camphor (see p. 266 and Scheme 23) followed by equilibration (by NaOMe and MeOH) of the mixture (4 : 1) of 3-exo-and 3-endo-methyl isomers [(32) and (33)] that is obtained. The final mixture contains -90% of 3-endo-methylcamphor, which is readily isolated by crystallization.…”

“…A minor isomeric product in the bromination of ( 33) is (+)-9-bromo-6-endo-meth ylisofenc hone (3 5a),5 and the formation of this compound from 3-endo-methylcamphor (33) or by rearrangement of 9-bromo-3-endo-methylcamphor (34) can be rationalized by the sequence of transformations that is shown in Scheme 7 [cf. path (B) in Scheme 41.…”

“…path (B) in Scheme 41. Thus, intermediate (3Oc) [derived from (33) or from (34)] could undergo 2,bhydride shift and subsequent rearrangement to produce (35a) (Scheme 7). An alternative Wagner-Meerwein rearrangement of intermediate (30c) [cf.…”

Reaction of Singlet Oxygen with 2‐Methylnorborn‐2‐ene, 2‐Methylidenenorbornane, and their 7,7‐Dimethyl Derivatives. The transition state geometry for hydroperoxidation

“…: 076 do, 97% d,, 30,; d,. (14). , 4 solution of 20 g (Cl.19 mul) of norbornanone and 240 ing (6 mmol) of KaOI-1 in 80 ml dioxane and 40 g D,O was heated t o 45' for 6 days.…”

“…To a stirred suspension o f 4.8 g (0.2 mol) magnesium turnings in 200 in1 ctlier was added a solution 01 30 g (0.21 mol) methyl iodide in 20 ml ether. The resulting Grignavd solution was treated dropwise with 14.2 g (0.066 mol) l-brotno-7,7-dimcthyltiorbornanone (16) [14] in 200 nil of ether. The mixture was stirred a t room t e npcrature for 5 h and then hydrolysed with a saturated aqueous ammonium chloride solution.…”