Synthetic approaches towards a series of bicyclo(1.1.1)pentylcarbenes and novel bicyclo(1.1.1)pentanes derived from (1.1.1)propellane

The synthesis of several bicyclo (1.1.1) pentylcarbenes derived from (1.1.1) propellane (1) was undertaken to investigate the stability of the carbenes compared to their tendency to rearrange. The penultimate precursors to the parent bicyclo (1.1.1) pentylcarbene (40) and bis(bicyclo- (1.1.1) pentyl)carbene (44) were synthesized. In addition, bicyclo (1.1.1) pentyl-chlorodiazirine (78) and bicyclo (1.1.1) pentylbromodiazirine (79) were synthesized. Preliminary results for solution studies and theoretical investigations are reported. In the context of these investigations, economical, reproducible, high-yielding, and large-scale syntheses of 3-chloro-2-(chloromethyl)-1-propene (4) and 1,1-dibromo-2,2-bis(chloromethyl)cyclopropane (5) have been developed. Additionally, a novel purification of (1.1.1) propellane (1) is reported which facilitates photochemical and nucleophilic additions to 1. The synthesis of 1,1-dichloro-2,2-bis(chloromethyl)cyclopropane (14) is reported as an alternative precursor to (1.1.1) propellane (1). Studies were undertaken to determine the most efficient means of preparing 1 from both precursors, 5 and 14. A multi-gram scale synthesis of 1-bicyclo (1.1.1) pentanecarboxylic acid (46), a key intermediate in the synthesis of the bicyclo (1.1.1) pentylcarbene precursors and other bicyclo (1.1.1) pentanes, was developed by modifying the reductive cleavage-carboxylation of bicyclo (1.1.1) pentyl phenyl sulfide (2) first reported by Wiberg and Waddell. Thus, the current preparative-scale synthesis of 1-bicyclo (1.1.1) pentanecarboxylic acid (46), published, in part, by Michl, Della, and Barton, has been condensed from nine steps to three steps from 1,1-dibromo-2,2-bis(chloromethyl)cyclopropane (5), with an overall yield of greater than 55%. Facile entry into the bicyclo(1.1.1) pentane system via the rich chemistry of (1.1.1) propellane (1), and more convenient access to multi-gram quantities of 1-bicyclo(1.1.1) pentylcarboxylic acid (6) have permitted significant progress to be made towards the synthesis of several novel bicyclo(1.1.1) pentanes. The current work was undertaken to investigate the physical and chemical effects of the strained bicyclo(1.1.1) pentane ring in various compounds. In this context, efforts towards the synthesis of several 1,3-disubstituted-bicyclo(1.1.1) pentanes are reported as substrates for polymerization studies. Synthetic approaches towards novel bicyclo(1.1.1) - pentylpaddlanes are reported, and the synthesis of bicyclo(1.1.1) pentylbis-carbene precursors is presented. The syntheses of tetrakis(bicyclo(1.1.1) -pentyl)methane (166) and tetrakis(bicyclo.(1.1.1) pentyl)ethylene (158) also were undertaken. The steric constraints of the corresponding tert-butyl compounds have frustrated efforts to synthesize those molecules. It was hoped that the less bulky bicyclo (1.1.1) pentyl ring would enable the synthesis of 158 and 166 to be achieved. This work continues. Finally, efforts towards determining an A-value for the bicyclo (1.1.1) pentyl group, and the gas phase acidity of the bicyclo (1.1.1) pentyl anion are reported