A selection of pseudo-geminally substituted [2.2]paracyclophanes, the alkynes 6, 7, 10, 11 a, and 11 b and the alkenes 8 and 9 were prepared for the study of intraannular reactions between functional groups in direct juxtaposition. Whereas 9 and 10 provide the corresponding cyclobutane and cyclobutene derivatives on irradiation (12 and 13, respectively), the bis-alkynes 7 and 11 b do not lead to a cyclobutadiene intermediate. In the latter case the "half-closed" butadiene derivative 17 was isolated. A Paterno-Büchi reaction took place on irradiation of 8 and 6, although the oxetene intermediate 21 produced in the second example did not survive the reaction conditions (ring-opening to 22). Bromine addition to 9, 10, and 7 occurred with high stereoselectivity (formation of the dibromides 27, 30, and 33, respectively), and is rationalized by postulating the formation of the cationic intermediates 26, 29, and 32, respectively. To study the interaction of a carbocation with a facing triple bond, the alcohol 34 was prepared from 6. On acid treatment ring closure to the triply-bridged phane 38 took place, accompanied by the hydration of the triple bond to the ketoalcohol 37. In an interesting intraannular [2+3]cycloaddition reaction the bis-acetylene 11 a, on treatment with n-butyl lithium, provided the cyclopentadiene derivative 42. That the two triple bonds of a pseudo-geminal diacetylene can engage in a cyclization reaction leading to the cyclopentadienone complex 44 was also shown by treating 11 b with iron pentacarbonyl.

No abstract

1990. 4, 668. A n p i . . ('hem Inr Ed. Enyl. 1995, 34, No. 6 1'8 VCH ~,r/ug.s~e.sell.~rhuft mbH, 0-69451 Weinheon, I995 o570-083sjP5lfls0n-068S $ 1O.ilOf ..?5/il

No abstract

In order to transfer the so-called topochemical control established by Schmidt and coworkers to fluid solutions, the [2.2]paracyclophane framework was substituted with two acryloyl substituents, one on each of the two decks. The 4 products thus formed are termed cinnamophanes. The pseudo-gem derivative, 1, was shown to undergo a very efficient stereospecific [2 + 21 photocycloaddition to form 5 with the highest quantum yield (=0.8) ever observed for such a Cinnamates are of great interest and under current investigation because of their use as chromophores for the design of photoactive polymers, molecular assemblies, supramolecular devices and UV It is well-known that cinnamic acids and cinnamate derivatives photodimerize or photopolymerize in the crystalline state according to the topochemical rules established by Schmidt and coworkers [*]. In contrast to the solid, the fluid solutions (and low viscosity media) are conducive mainly to trans-cis isomerizati~n [~]. Dimerization becomes significant only when the chromophores are held together by a However, even then, several intramolecular photodimers are generally observed, associated with the dynamic and conformational properties of the molecular skeleton[g-' 1. Furthermore, in the crystal, for a P-type stacking, the yield of the dimerization cannot be quantitative for statistical reasonsL2I; the maximum value would never exceed 86% even for a perfect single crystal transformation occurring without any destruction of the crystalline habitrn.It was anticipated that topochemical reaction control could be transferred to fluid solutions if the reactive centres were held in a given mutual orientation within a rigid molecular framework.The [2.2]paracyclophane skeleton fulfills this requirement: with acryloyl substituents, the pseudo-gem compound 1 is reminiscent of the P-type stacking of trans-cinnamic acids in the crystal. Comparison of the photochemical properties of 1 with those of its isomers 2, 3 and 4 should bring new insights into bimolecular interactions between cinnamates.