53 Very often different behavior is observed in the decomposition of tosylhydrazones of aliphatic ketones under protic or aprotic Bamford–Stevens conditions. 56 Possible mechanisms in the formation of these products are in agreement with previous mechanistic conclusions concerning tosylhydrazone decompositions. The tosylhydrazone ( 63), bearing an adjacent cyclopropyl group, decomposes on treatment with sodium methoxide in ethylene glycol to give four alkenic products (equation 44).

Ethylene glycol is the most popular and reliable solvent. The original Bamford–Stevens reaction employs protic solvents in the decomposition of a tosylhydra- zone with a strong base. 125 These examples clearly illustrate that predicting regioselectivities in the aprotic Bamford–Stevens reaction without extremely close precedent is treacherous. 124 In some cases, it is the less substituted regioisomer that predominates, as illustrated by one step in the synthesis of azaprostaglandin analogs ( Scheme 62). 121 There are, however, isolated examples of excellent selectivity, such as the reaction of a 3-ketotetrahydrofuran tosylhydrazone salt to give the corresponding cyclic enol ether as the major product ( Scheme 61), 122 the introduction of a Δ 7 double bond in a steroid skeleton, 123 and the exclusive formation of the more highly substituted alkene regioisomer in a terpenoid decalin ring system ( Scheme 61). A key step in the synthesis of (+)-α-eudesmol and (–)-α-selinene exemplifies this point ( Scheme 60). 120 Further, even for cases in which elimination to an alkene is the predominant pathway, the regioselectivity of the process is often mediocre. The protic reaction on occasion is a useful method of alkene formation, but is far from general because the cation intermediate tends to undergo rearrangements.

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