Sommelet-Hauser reaction

Klunder nicely exploited the Sommelet-Hauser reaction to synthesize dipyridodiazepine derivatives, such as 84, whose structural analogues show potent inhibition of HIV-1 reverse transcriptase.42 The key step here involves a [2,3]-sigmatropic rearrangement across the pyridine ring. 

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

In 1930, Ingold and Jessop reported the rearrangement of the fluorenyl ylide (412).Compound (414) was obtained in what can be considered as the first example of a Sommelet-Hauser reaction (Scheme 106). In 1937, Sommelet described the base-catalyzed transformation of the benzhydryl ammonium bromide (415) into the substituted benzylic amine (416 Scheme 107, equation a)." Wittig found later that reacting the salt (417) with phenyllithium produced two amines, (418) and (419). The former is derived from a Sommelet-Hauser 3,2-rearrangement, whereas the latter comes from a Stevens... 

Several limitations of this base-promoted rearrangement are worthy of mentioning (a) when structurally feasible, both Stevens and Sommelet-Hauser reactions will compete (b) certain substituents on the aromatic ring, e.g. Cl, CN, NO2, prevent the formation of the ylide and no rearrangement takes place (c) if a p-hydrogen is present on the ammonium salt, elimination becomes yet another undesirable side reaction, In an attempt to overcome these limitations, Sato has utilized the fluoride-induced desilylation of... 

In 1992, Smith and his group described the total synthesis of indole diterpenes (+)-paspalicine and (+)-paspalinine based on the use of Sommelet-Hauser reaction for the formation of the polycyclic indole... 

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

Selective o/t/io-acylation and orrfio-formylation of 2-alkyl pyridines is possible by [2,3] sigmatropic rearrangement (Sommelet-Hauser) of a-pyrrolidinyl-2-alkylpyridine sulfonates (268), prepared by treating the parent base with cyanomethyl benzenesulfonate (76JOC2658). Acid hydrolysis of the rearranged product (269 R = H) yields 3-formyl-2-methylpyridine (270). Methylation of (269 R = H) using NaH-Mel and acid hydrolysis of the reaction mixture gives 3-acetyl-2-methylpyridine (270 R = Me). 

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). 

Reaction of benzyne with tertiary aliphatic amines to give anilines via Sommelet-Hauser and/or Stevens-type rearrangements of the intermediate ylid has been documented.362 363... 

Modification of the stereochemistry of the reaction has been demonstrated by studying desilylation reaction of cis- and mmy-2-methyl-1 -(phenyl)isoindolinium 2-methylides. It has been established that cw-isomer leads preferentially to the Sommelet-Hauser rearrangement product (eight-membered ring formed) whereas the trans-isomer leads predominantly to the Stevens rearrangement product.374... 

Otter et al. (89JHC1851) obtained the thienopyrimidine 253 in 50% yield by heating 5-(2-propynylthio)pyrimidine 248 in DMSO at 145°C. The reaction proceeds via a Claisen rearrangement of 248 in the allene 249, which then cyclizes to the product 253. An 18% yield of the thiomethyl compound 252 was also isolated. This was explained by a mechanism involving solvent incorporation into allene 249 to give intermediate 250 this intermediate then undergoes a Sommelet-Hauser type of rearrangement to afford 251, which cyclizes to the product 252. 

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. 

Lactams participate in a number of ring enlargement reactions of different types. Because of the classification in this review they are described at other places too e.g. Sommelet-Hauser rearrangement (Chapter V3). 

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