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The [2+2+2] cycloaddition strategy is complementary to the well known Diels-Alder reaction for the generation of polycyclic compounds. This [2+2+2] approach is atom-economical and, with the availability of new catalysts to effect the [2+2+2] cycloaddition reaction, synthesis of a wide variety of highly functionalized polycycles is possible. This review deals with some recent advances relating to [2+2+2] cycloaddition reactions involving the syntheses both of polycycles

The design and synthesis of spirocycles is a challenging task because it involves the creation of a quaternary center, which itself is considered to be one of the most difficult tasks among synthetic transformations. Some recent approaches based on metathesis, cycloaddition and transition-metal-mediated transformations to spirocycles are described here.

The photochemically induced Wolff rearrangement has proved to be an excellent method for the preparation of BCB derivatives-by a ring contraction protocol-which are otherwise dif®cult to prepare. Thus, the a-diazoindanones 48 undergo a ring contraction reaction under a Scheme 13. Scheme 14. Scheme 15. Scheme 16.

The most stable is not necessarily the most easy to obtain! Two new stable crystal forms of the 120 year old compound sym‐trinitrobenzene are reported. These elusive forms have been obtained by the use of an additive, trisindane, that can act as a mimic in the crystallization experiment (see scheme).

The building block approach was identified as a useful alternative to the commonly used Bücherer-Berg method for the preparation of cyclic unusual alpha-amino acid derivatives. The symmetrical building blocks were prepared by dialkylation of ethyl isocyanoacetate under solid-liquid phase transfer catalysis conditions while the unsymmetrical building blocks were prepared by a stepwise alkylation of the O'Donnell Schiff base. Metathesis reactions, Suzuki couplings, and cycloaddition reactions were utilized to assemble the building blocks.

SummaryIn this review we cover various approaches to meta- and paracyclophanes involving popular reactions. Generally, we have included a strategy where the reaction was used for assembling the cyclophane skeleton for further functionalization. In several instances, after the cyclophane is made several popular reactions are used and these are not covered here. We included various natural products related to cyclophanes. To keep the length of the review at a manageable level the literature related to orthocyclophanes was not included.

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