Cyclobutyl radicals synthesis

A cydization/Barbier-type reaction was reported by Curran and coworkers [21] in 2004 in the total synthesis of penitrem D 46. In this work, the aryl radical generated from the iodoarene 41 and Smij proceeded to attack the tethered cyclobutene to from a cyclobutyl radical 42. Subsequently, reaction with Smij led the organo-samarium species 43, which underwent a Barbier-typie reaction with acetone to give the tertiary alcohol 44 in 40% yield. The product contains the BCD ring system of penitrem D 46 (Scheme 5.12). 

The main product is pinane hydroperoxide (2) which can be reduced to 2-pinanol (3), an important intermediate in the industrial synthesis of linalool [1, 2, 3]. Pinocampheol (4), verbanol (5), pinocamphone (6) and verbanone (7) are also formed in minor amounts. When the reaction is carried out at temperatures higher than room temperature, pinane hydroperoxide is decomposed. It yields mainly the monocyclic products bearing the cyclobutyl ring (9 - 12) (Figure 1) [1], These products result from the fragmentation of the 2-pinanyloxy radicals which in turn result from the decomposition of 2-pinane hydroperoxide [1]. 

Crimmins, M. T., Wang, Z., and McKerhe, L. A., Rearrangement of cyclobutyl carbinyl radicals total synthesis of the spirovetivane phytoalexin ( )-lubiminol. Tetrahedron Lett., 37, 8703-8706, 1996. 

---