41. Parthenolide undergoes " trans "-annular cyclization and elimination to form the guaianolide skeleton. 42. A diol can be converted to cyclic ether by using an acid catalyst, this is diol cyclization . 43. A similar reaction is the reductive cyclization of enones to form the corresponding alcohol in a stereoselective manner. 44. Squalene, through a cyclization reaction with 2, 3-oxidosqualene 6 as an intermediate forms cycloartenol. 45. The implication of different reaction is that cyclization needs to occur in a concerted step with enol formation. 46. This tunnel aided intramolecular aldol condensation provides the first cyclization when the chain is still in the tunnel. 47. Through radical cyclization a five membered ring is formed followed by the propagation of a new tin radical. 48. The ylide reacts with the electrophilic ester trap through intramolecular cyclization to form a five-membered ring. 49. The racemic synthesis involves addition / cyclization reaction of 2-amino-1-phenylethanol with cyanogen bromide. 50. However, even lab syntheses of isoquinolines has been performed by cyclization of ( acylated derivatives of ) phenethylamine.
