On the supposed “2-chlorobenzocyclopropene”

The Cycloproparenes

“…The products were originally (27) assigned as 2-bromo-and 2-chlorocyclopropabenzene 29a,b and their formation rationalized by the pathway shown in Scheme IV which involves dihalocycloheptatriene intermediates. However, the structural assignments were subsequently shown to be incorrect and the products have been reassigned as the 3-halo derivatives 30a,b (28)(29)(30). Thus the dehydrohalogenation of 28 does not involve skeletal rearrangement (30) and is fully compatible with the Billups-Giinther mechanism of Scheme III.…”

“…The additions of mineral acids and halogens to cycloproparenes to give arylmethyl derivatives continue to be used for characterization purposes (34,39), although the direction of ring opening of 43 with iodine is not settled (40). The reaction between 30b and hydrochloric acid yields a 3.5:1 mixture of 3-and 4-chlorobenzyl chloride (28) in contrast to the silver(I) catalyzed methanolysis which yields only the corresponding 4-chlorobenzyl ether (29). On the other hand only 67 is obtained from 43 with acid (40) and it would seem that the influence of substitution patterns on the direction of ring cleavage in the unsymmetrical cycloproparenes is in need of more detailed examination.…”

The Synthesis and Reactivity of 5H-Cycloprop[f]isobenzofuran and Related Compounds. A Kinetic Probe for the Mills-Nixon Effect

“…The k 2 values for the addition of dimethyl fumarate to the linearly ring-fused or disubstituted isobenzofurans (32a-e) as well as the angularly cyclobuta-fused derivative (35) are given in Table 2. The rate data reveal (25) (32)…”

“…5 . The angularly fused cyclobuta-derivative (35), which loses T-bond order across the bridged bond in going from reactant t o transition state, should be more reactive than ( I ) , whereas it actually has the same reactivity as (1). It also is slighty less reactive than the linearly fused isomer (32c), although the operation of the Mills-Nixon effect would demand it to be more reactive.…”

“…Hence the kinetic probe used in this study rules out that T-bond fixation in the direction indicated by general structure (7a) is significant for adduct (8). The similarity in reactivity of the cyclobuta-fused isobenzofurans (32c) and (35) also rules against the operation of a Mills-Nixon effect in these systems.…”