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2,2-Dimethoxy-3,3-dicyanospiro[cyclopropane-1,9'-[9H]fluorene] reacted fast with methanol to afford 9-trimethoxymethyl-9-dicyanomethyl-9H-fluorene. Reaction with benzaldehydes also gave products of cyclopropane ring opening. Strong electron-donor p-substituents or a strong attractor enhanced the rate. Ring opening of the cyclopropane to a zwitterion that recloses or reacts with an aryl aldehyde, to form either a CO or a CC bond first, can explain the result. The former mode of closure is sensitive to p-substituents because they are directly conjugated to the positive charge at the benzylic carbon of the former aldehyde. The latter mode is sensitive to the ground-state electrophilicity of the carbonyl carbon of the former aldehyde. Thus, reaction of the cyclopropane with p-substituted aldehydes is accelerated by either electron-donor or -acceptor substituents. [reaction: see text].

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Addition reactions Addition reactions O 0060Regioselective Aminobromination of Terminal Alkenes. -Several N-Boc-2-bromoamines are prepared by a two-step method involving the reaction of new dibromocarbamate (II) with terminal alkenes to give N-bromo-N-Boc adducts, which are reduced in situ. Deprotection of these N-Boc products by treatment with HCl or TosOH affords the corresponding ammonium salts in pure state and good overall yields. The observed regioselectivity of the aminobromination for anti-Markovnikov addition is fully consistent with the radical-chain mechanism proposed for the reaction. -(SLIWINSKA, A.; ZWIERZAK*, A.; Tetrahedron 59 (2003) 31, 5927-5934; Inst. Org. Chem., Tech. Univ., PL-90-924 Lodz, Pol.; Eng.) -Klein 45-036