Sultone rearrangements. I. 10-Isobornyl and 4-methyl-10-isobornyl sultones

Abstract

Thermal rearrangement of 10-isobornyl sultone (1) affords exo-camphene sultone (2). In the early stages of the rearrangement endo-camphene sultone (8) can be isolated. The stability order for the sultones appears to be 2 > 8 > 1. Two mechanisms are postulated to explain the transformation. One involves an endo-3,2-methyl shift and the other involves a circuitous route of an exo-3,2-methyl shift and several Wagner-Meerwein and 6,2hydride shifts. A preparation of 4-methyl-10-isobornyl sultone (18) from either camphor or fenchone is described. Sultone 18 rearranges to an endo sultone (29) at moderate temperatures, but the only product found at higher temperatures is an aromatic hydrocarbon, 3,4-dimethylcumene (35). Mechanisms are proposed to account for the aromatization reaction.A few years ago we discovered a unique thermal rearrangement of a sultone.1 Upon being heated to its melting point, 10-isobornyl sultone (1) rearranges to ezo-camphene sultone (2). It was subsequently found that solid 1 can be transformed to solid 2 at temperatures below the melting point of 1.Two mechanisms can be envisioned to explain the transformation: (A) an exo-3,2-methyl shift involving several steps or (B) an endo-3,2-methyl shift involving only a couple of simple steps. These mechanisms are

Unified Synthesis of 2‐Isocyanoallopupukeanane and 9‐Isocyanopupukeanane through a “Contra‐biosynthetic” Rearrangement

“…[28] Furthermore, simple sultones have been formed through the addition of electrophilic SO 3 across an alkene followed by Wagner-Meerwein type rearrangements. [29] Ultimately, we were able to improve upon our initial observation by accessing sultone 14 directly from alcohol 13 upon treatment with a mixture of H 2 SO 4 and AcOH. This alternative sequence avoided the isolation of volatile allopupukeanene 7.…”

Synthesis and Structural Characterization of Novel Camphor‐derived Amines

“…The letter was formed as a racemate ([α] D r.t. = 0, centrosymmetric space group ( P 2 1 / a ) of the single crystal used for X‐ray analysis). Although mechanistic investigations of the camphene sultone have been studied, we could, so far, not explain the formation of the closely related sultone 12 (and of 11 ) (Scheme ).…”

Chiral Lewis Acid-Mediated Enantioselective Pictet−Spengler Reaction of Nb-Hydroxytryptamine with Aldehydes

“…We next examined other chiral dialkylchloroboranes, such as dialkylchloroboranes 11 and 12 prepared by hydroboration of the corresponding chiral alkenes 13 and 14 with H 2 BCl·SMe 2 , which were used without purification. Compared to the reaction with (−)-Ipc 2 BCl, although the reaction of 1 catalyzed by 11 or 12 proceeded quantitatively, it gave poor enantioselectivity (less than 5% ee).…”