Regioselectivity and Stereospecificity in a Contrastereoelectronically Controlled Pinacol Rearrangement of Alkoxycyclobutane Derivatives. A Novel Route to Vicinally Substituted Cyclopentanones
作者:Debasis Patra、Subrata Ghosh
DOI:10.1021/jo00113a036
日期:1995.4
A four-step sequence for the synthesis of vicinally substituted cyclopentanones 5 and 9 has been developed starting from the acyclic ketones 1. The key step involves a stereospecific pinacol-type rearrangement of the cyclobutane ring embodied in oxabicyclo[3.2.0]-heptanes 4 and 8 involving exclusive migration of the stereoelectronically disfavored cyclobutane bond. The oxabicyclo[3.2.0]heptanes have been obtained by copper(I) triflate (CuOTf) catalyzed intramolecular photocycloaddition of the dienes 3 prepared from the ketones 1 on reaction with (ethoxyvinyl)lithium followed by allylation of the carbinols 2. The regioselectivity observed in bond migration has been attributed to be the result of the stabilization of the cation 15 by the neighboring hydroxyl group that is generated during the rearrangement.
Intramolecular [2+2] photocycloaddition — cyclobutane rearrangement. A novel stereocontrolled approach to highly substituted cyclopentanones
作者:Subrata Ghosh、Debasis Patra、Susanta Samajdar
DOI:10.1016/0040-4039(96)00195-5
日期:1996.3
A simple stereocontrolled route involving intramolecular [2+2] photocycloaddition followed by rearrangement of the resulting cyclobutane derivatives is described for the construction of cyclopentanones with substituents upto three contiguous chiral centres.
Stereocontrolled approach to highly substituted cyclopentanones. Application in a formal synthesis of Δ9(12)-capnellene
作者:Susanta Samajdar、Debasis Patra、Subrata Ghosh
DOI:10.1016/s0040-4020(97)10387-8
日期:1998.2
copper(I)-catalysed stereoselective photocycloaddition of the dienes 6a-d followed by stereospecific rearrangement of the cyclobutane derivatives 7a,b, 8 and 9. Employing this methodology a formal synthesis of the sesquiterpene Δ9(12)-capnellene 2 has been achieved.