Ring Expansion of Isopropenylcyclopropanes to Dihydromethyloxepins

Abstract

The stereochemistry was studied concerning the ring expansion of some 2-isopropenylcyclopropane-1-carbonyl compounds to 2,5-dihydro-3-methyloxepin derivatives. The LAH reduction of dimethyl 2-isopropenylcyclopropane-1,1-dicarboxylate (1aa) gave the corresponding diol, and a subsequent Swern oxidation gave a seven-membered 4,7-dihydro-6-methyloxepin-3-carbaldehyde. A DIBAL reduction of 1aa gave two isomeric hydroxymethyl carboxylic esters, and a subsequent Swern oxidation of methyl 1-hydroxymethyl-t-2-isopropenylcyclopropane-r-1-carboxylate caused a ring expansion to give methyl 4,7-dihydro-6-methyloxepin-3-carboxylate; however, a similar Swern oxidation of methyl 1-hydroxymethyl-c-2-isopropenyl-cyclopropane-r-1-carboxylate caused no ring expansion to give methyl 1-formyl-c-2-isopropenylcyclopropane-r-1-carboxylate.

One‐Pot Synthesis of Metastable 2,5‐Dihydrooxepines through Retro‐Claisen Rearrangements: Method and Applications

“…The computational studies support the experimental resultsa nd can explain the reactivity differenceo bserved between substrates derived from cyclic or linear 1,3-diketones.T his study thus complementst he chapter on this powerful rearrangement discovered in the 1960s. [1][2][3][4][5][6] Importantly,t his one-pot retro-Claisen rearrangement was applied to the total synthesis of the natural product radulanin A. Its phytotoxic properties were demonstrated for the first time validating our allelopathich ypothesis and paving the way to the development of natural herbicides, which may have better environmental profiles than those currently used.…”

Synthesis and polymerization of vinylcyclopropanes

“…They are very stable against reducing agents, e. g., LiAlH 4 . Consequently, carboxy-functionalized VCPs can be easily transferred into the corresponding hydroxymethyl derivatives 60) . In contrast, VCPs tend to decompose under oxidizing conditions.…”

The Retro‐Claisen Rearrangement of 2‐Vinylcyclopropylcarbonyl Substrates and the Question of its Synthetic Potential

“…on, the retro-Claisen rearrangement of 2alkynylcyclopropane carboxaldehydes (29) was first reported by Chuche in 1979. It may be synthetically useful for the synthesis of oxepine rings, but it has never been exploited.…”

“…Furthermore, marked differences can be observed depending on the nature of substituents on position 1 (Scheme 8b and c). 19,29,30 Carbonyl substituents would destabilize the cyclopropanecarboxaldehyde form, through dipole repulsion, favoring the retro-Claisen rearrangements towards 52, 55 or 57. The rearrangement was not observed in the case of a chloromethyl substituent in 53.…”

“…The rearrangement was not observed in the case of a chloromethyl substituent in 53. 29 Substituents on the vinyl group have also a dramatic effect on the reaction equilibrium. In particular, substituents stabilizing zwitterionic transition state 44 would favor the Cloke-Wilson rearrangements instead of the concerted retro-Claisen process.…”