Substituent Effects and Nearly Degenerate Transition States:  Rational Design of Substrates for the Tandem Wolff−Cope Reaction

Abstract

Su, Sarpong, Stoltz, and Goddard -Supporting Information S1# Ball-and-stick figure Level of theory/basis//HF (hartree), ∆G correction (kcal/mol) from calc. real frequencies; λ 1 , λ 2 (two lowest eigenvalues, transition structures)

Toward a Symphony of Reactivity: Cascades Involving Catalysis and Sigmatropic Rearrangements

“…[18] Sonication of diazo ketone 32 with a catalytic amount of AgOBz and a stoichio-metric amount of Et 3 N at 45°C led to the desired cycloheptadienone 34 in excellent yield (Scheme 8). Under photo-lytic conditions, the success of the reaction was mixed.…”

“…[17] Two authors of this review expanded the strain-release Cope rearrangement to ketene substrates and developed a Wolff/Cope rearrangement duet. [18] Sonication of diazo ketone 32 with a catalytic amount of AgOBz and a stoichiometric amount of Et 3 N at 458C led to the desired cycloheptadienone 34 in excellent yield (Scheme 8). Under photolytic conditions, the success of the reaction was mixed.…”

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

“…The group of Stoltz [196–197] succeeded in establishing a tandem Wolff rearrangement/divinylcyclopropane rearrangement strategy [198]. Readily accessible α-diazo ketone 234 (see Scheme 28) was shown to undergo Wolff rearrangement [199] upon treatment with silver benzoate.…”

Table of Contents

“…This lack of reactivity is likely due to an unfavorable interaction with the cis ‐R group in the transition state of the [3,3] rearrangement, significantly slowing the rate of this pathway 16. 17 The fact that none of the dihydroazepine was observed in this particular case strongly suggests that a concerted mechanism is operative for the rearrangement, as the increased flexibility of a ring‐opened zwitterionic intermediate (as shown in Path B or C) should still allow the cyclization to occur. Notably, the formation of such zwitterionic intermediates should not be hampered by the steric hinderance of the distal alkenyl moiety in either 1 k or 1 l .…”