Polymers Containing Ring-Strain Energy. 1. New Monomers and Polymers Based on Cyclopropane, Norbornadiene, and Quadricyclane

Article abstract of DOI:10.1021/jo00067a055

The synthesis and polymerization chemistry of 1,1-bis(XCH2)cyclopropane <1, X=OH; 4, X=I> was studied.Treatment of 1 with base in the presence of α,ω-dihalides did not produce a polyether.However, treatment of 4 with the bis(alkoxide) derived from hexanediol afforded a polyether of low molecular weight n=3000, PD=3>.A general method for alkylating norbornadiene in the 2-position was developed.Treatment of norbornadiene with tert-BuOK, tetramethylethylenediamine (TMEDA), n-BuLi, and tributylchlorostannane (in that order) afforded 2-(tributylstannyl)norbornadiene in excellent yield.On the other hand, carbon electrophiles < e.g. bromobutane, 1,4-dibromobutane, and 2,3-dichloropropene> required the generation of the 2-(lithiocyanocuprate) in order to effect clean alkylation.Treatment of 2-<3-(2-chloropropenyl)>norbornadiene (8a) with RMgX in the presence of (dppp)NiCl2 afforded the cross-coupling products 2-(XCH2)-norbornadiene <9, X=2-buta-1,3-dienyl; 10, X=α-styryl; respectively> in high yield.Polymerization of 9 in THF initiated by n-BuLi resulted in an elastomeric polymer (12) n=18,000, PD=1.5>.Photolysis of 12 in the presence of (Ph3P)2CuBr converted the pendant norbornadiene to quadricyclane (13).Heating of the photoisomerized sample to 180 deg C caused an exothermic (by DSC) reaction which corresponded to 59percent of theory (using the value 26 kcal/mol: quadricyclane -> norbornadiene).