Michael reaction pericyclic reactions

In our previous book on domino reactions [4h], we have classified domino reactions according to the mechanism of the different steps. This organizing principal will also be used in this book, and you will find chapters about transition metal catalysis including carbonylation, metathesis and CH-activation, nucleophiHc substitutions, radical reactions, pericyclic reactions, Michael reactions, aldol reactions, oxidations, and reductions. 

Altenbach used the Michael addition of sodium methyl malonate to allene (206) for a dia-stereoselective spiroannulation to a steroid (equation 72). Or, in imaginative work by Okamura, allenyl sulfoxides were transformed into enantiomerically pure hydrocarbons by pericyclic reactions like electrocyclic ring closure (equation 73) or intramolecular cycloaddition (equation 74). Note that the starting materials (propargylic alcohols) are readily accessible as single enantiomers. 

Dewar, Michael J. S., 8c Ramsden, Christopher A. 1974. "Stevens Rearrangement. Antiaromatic Pericyclic Reaction." Journal of the Chemical Society, Perkin Transactions 1 1839-1844. 

The [2+2] cycloaddition is the main method for the synthesis of cyclobutanes and 4-membered ring heterocycles. The thermal reaction between two alkenes is not a synchronous, pericyclic process, which is symmetry forbidden, but is a two-step, Lewis acid-catalysed procedure involving a Michael reaction between an electron-rich alkene and an electron-poor partner followed by cyclisation (Figure 8.7). 

The HX compounds are electrophilic reagents, and many polyhalo and polycyano alkenes, (e.g., Cl2C=CHCl) do not react with them at all in the absence of free-radical conditions. When such reactions do occur, however, they take place by a nucleophilic addition mechanism, (i.e., initial attack is by X ). This type of mechanism also occurs with Michael-type substrates C=C—Z, where the orientation is always such that the halogen goes to the carbon that does not bear the Z, so the product is of the form X—C—CH—Z, even in the presence of free-radical initiators. Hydrogen iodide adds 1,4 to conjugated dienes in the gas phase by a pericyclic mechanism ... 

If a carbonyl group is attached a to position 1 of the pericyclic system, the oxy-Cope rearrangement of divinylcyclohexanes results in the formation of medium ring enolates, which after proton transfer undergo a transannular vinylogeous aldol-type reaction (probably a transannu-lar, intramolecular Michael-type reaction). For example, tricyclic alcohol 4 is obtained via such a reaction sequence from 1 in 45% yield1129. 

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