Sommelet ring expansion

In a base-catalyzed ring expansion route to 1,2-diazocines, Sommelet-Hauser rearrangement of the A-amino derivative of nicotine (22) using sodium in ammonia afforded pyrido-l,2-diazocine 23. The reaction was regiospecific, i.e., no isomeric 24 was detected (82H1595). 

V. The Cope Rearrangement, the [1.3] Sigmatropic Shift, the Sommelet-Hauser Reaction, and Sulfur-Mediated Ring Expansions... 

V3. Sommelet-Hauser Rearrangement and Sulfur-Mediated Ring Expansion... 

The Sommelet-Hauser rearrangement has rarely been used as a tool in organic synthesis and then only for very special systems [54], The reason is undoubtedly that the Hofmann elimination and the dealkylation reaction of quaternary nitrogen atoms are in direct competition with the ring expansion reactions of these substrates. 

In some cases ring expansion has been obtained during the Sommelet-Hauser rearrangement (refs. 94, 100). This rearrangement also occurs with naphthalenic derivatives (Fig. 18) and with many other heterocyclic compounds (refs. 105-107). 

Finally in this section, two papers concerning the synthesis of larger rings are worthy of mention. The Sommelet-Hauser rearrangement has been utilized in the transformation of a wide variety of heterocycles. The reaction has now been applied to the ring-expansion of nicotine, giving the pyridodiazocine (203) as... 

The Sommelet-Hauser reaction, a [2, 3] sigmatropic rearrangement of ammonium ylides, is also an attractive method for ring expansion of nitrogen heterocycles. Recently... 

Figure 13 Competition between the Sommelet-Hauser (top) and Stevens (bottom) rearrangements in the ring expansion of nitrogen heterocycles...

---