Dinitrobenzoate solvolysis

Some of the evidence for the bisected cyclopropylcarbinyl cation follows. That the charge can be delocalized to both C2 and C3 simultaneously has been shown by the work of Schleyer and Van Dine.81 These workers studied the solvolysis of cyclopropylcarbinyl 3,5-dinitrobenzoates and found that methyl substituents accelerated the rate by an amount dependent only on the number of such substituents and not on their position. Thus 68, 69, and 70 react at almost the same rate. If the transition state for ionization were similar to the bicyclo-butonium ion, two methyl groups at C2 should accelerate the rate more than one at C2 and one at C3. A symmetrical transition state for ionization similar to the bisected cyclopropylcarbinyl cation (67) in which the charge is delocalized over all four carbon atoms best explains the results. 

Evidence for the S pentadienyl ions has been obtained from kinetic and stereochemical studies on the solvolysis of dinitrobenzoate esters of dia-stereoisomeric alcohols like 22 and 23. An SN1 mechanism is suggested for the solvolyses, which proceed essentially with retention of configuration at C-l, (162-164,167). S-Shaped ions have also been observed directly by low-temperature NMR studies of the protonation of suitable alcohols. The normally rapid rearrangement of the S ion to the U ion is inhibited to some extent by destabilizing the U ion by introduction of an anti substituent (168) [Eq. (18)] or by constraining the S structure partly in a ring system (169). The... 

The solvolysis of MeS-4-0(S)CPh in aqueous/trifluoroethanol at 25 °C is zero-order in [N ].42 Fig. 4A shows that formation of MeS-4-N3 occurs at the expense of MeS-4-OSolv but not MeS-4-S(0)CPh. The reaction of MeS-4-(3,5-dinitrobenzoate) under the same conditions proceeds through the liberated carbocation intermediate MeS-4+ which partitions between addition of solvent to form MeS-4-OSolv and azide anion to form MeS-4-Nj.14 Fig. 4B shows that the yields of MeS-4-Nj, calculated as a fraction of the sum of the yields of MeS-4-Nj and MeS-4-OSolv, from the reactions of MeS-4-0(S)CPh and MeS-4-(3,5-dinitrobenzoate) are identical. These data show that essentially 100% of the ion-pair intermediate of reaction of MeS-4-(3,5-dinitrobenzoate) undergoes separation to the free carbocation which is trapped by azide ion, while 14% of the reaction of MeS-4-0(S)CPh proceeds by this pathway and 86% proceeds by the competing isomerization reaction.42... 

Schleyer and coworkers investigated the nature of the 9-barbaralyl cation by solvolysis studies of the corresponding tosylate. The acetolysis of 9-deuterio-9-barbaralyl tosylate gave 9-barbaralyl acetate with complete deuterium scrambling, whereas solvolysis in more nucleophilic aqueous acetone gave the product alcohols with the label exchanged to only positions C3, C7 and C9 (equation 50). Solvolysis of 4-deuteriobicyclo[3.2.2]nona-2,6,8-trien-4-yl 3,5-dinitrobenzoate also resulted in the formation of the 9-barbaralols with deuterium scrambled to positions 1, 2, 8, 4, 5 and 6, with only trace amounts at C3 and (equation 51). 

With the aim of studying a geometrically well-defined cyclopropylcarbinyl cation Baldwin and Foglesong (1968a) prepared the 8,9-dehydro-2-adamantyl 3,5-dinitrobenzoates [125 X = H, D or T]. The solvolysis of [125] in 60% aqueous acetone proceeded with considerable rate enhancement in comparison with 2-adamantyl tosylate. Scrambling of the label to the 8 and 9 positions in the solvolysis of [125 X = D] and [125 X = T] revealed a degenerate rearrangement (90) of the intermediate 8,9-dehydro-2-adamantyl cation [126]. 

Blair et al. (1972) solvolysed the deuterium-labelled benzobicyclo[3.2.2]-nonatrienyl dinitrobenzoate [445] in 80% aqueous acetone at 120°C. The solvolysis was accompanied by considerable deuterium scrambling. Of the deuterium, 45 % appeared at C(2) while 55 % was scrambled almost statistically amongst the remaining non-benzo positions in the barbaralol products (287). Similar results were obtained for the barbaralyl dinitrobenzoates (287). The unrearranged product alcohol also indicated that significant scrambling had taken place. The results show no unusual instability of the benzobicyclo-[3.2.2]nonatrienyl cation. 

An essentially additive effect of ring substituents on the 7r-donor ability of cyclopropyl in generation of carbocation derivatives was also shown in the solvolysis of a series of methyl-substituted cyclopropylcarbinyl dinitrobenzoates (ODNB) (equation 4) studied by... 

Brown and coworkers have published several papers concerning solvolyses of 1-aryl-1-cyclopropyl 3,5-dinitrobenzoates in 80 % aqueous acetone. A plot of log k versus <7 revealed, by its non-linearity, a change in mechanism as electron demand at the cationic center increases. The more electron-releasing substituents give more unrearranged cyclopropyl product. Thus the cyclopropanol to allyl alcohol ratios were p-MeO, 87 13 p-MeS, 70 30 and p-Me, 5 95. Extrapolation of the tertiary data to the parent cyclopropyl system indicates that solvolysis of the latter must be enhanced by concerted ring-opening by a factor of 10. ... 

Tabushi and coworkers " investigated the solvolysis of 1-quadricyclylcarbinyl 3,5-dinitrobenzoate (ODNB) (37) in 60 % aqueous acetone at 25°C which gave a mixture... 

As part of their key study of the reactivities of geometrically constrained cyclopropylcar-binyl systems, Rhodes and DiFate examined the solvolysis of the 2,4-trimethylene bridged 2-bicyclo[3.1.0]hexyl 3,5-dinitrobenzoate (71) in 50% ethanol. There is no other... 

The relative rates of solvolyses of the four isomeric 2-bicyclo[6.1.0]nonyl 3,5-dinitrobenzoates in 80% aqueous acetone are indicated below . For the cis ring-fused [6.1.0] derivatives 91 and 92, the rates of solvolysis are approximately half as fast as those of the corresponding [5.1.0] derivatives 87 and 88. As observed in the [5.1.0]system, endo... 

TABLE 1. Rates of solvolysis of some 2-bicyclo[n.l.O]alkyl 3,5-dinitrobenzoate esters in 80% aqueous acetone at 100 °C... 

Solvolysis of (l-methyl-2-methylenecyclopropyl)methylcarbinyl-3,5-dinitrobenzoates (105) in aqueous acetone in the presence of 2,6-lutidine led to C3 - C4 ring enlargement products (equation 75). ... 

The solvolysis of spiro[2.n]alkan-4-ol derivatives leads to ring enlargement products. In particular, solvolysis of spiro[2.3]hexyl-4-(3, 5 -dinitrobenzoates) (ODNB) (237) in 80% aqueous acetone gives a mixture of five-membered ring compounds derived from C3 - C5 ring expansion (equation 156) . 

The same products were obtained in the solvolysis of 4-chlorospirohexane 1-methyl-bicyclo [2.1.0] pentyl p-nitrobenzoate, 1-cyclobutenylethyl tosylate and l-methyl-bicyclo[ 1.1.1] pentyl dinitrobenzoate, suggesting that the bicyclo [2.1.0]pentane-1-methyl cation is the common intermediate. 

Thus the rates of solvolysis of various 3,5-dinitrobenzoates (ODNB) of 11-hydroxymethyl derivatives of [4.4.1]propellanes of different oxidation states all fall within a factor of 10 The same holds for various epimers of the same derivatives of 10-hydroxymethyl-(also on the bridge) derivatives of various [4.3.1]propellanes of different oxidation states. The rate difference between the extremes (50 and 51) was 80 The authors attribute the difference to conjugative factors . 

Alkyl substituents at C—1 of 2-adamantyl tosylate greatly increase the yield of 4-exo-protoadamantyl solvolysis products573. l-Methyl-2-adamantyl tosylate (869) and 4-methyl-4-exo-protoadamantyl dinitrobenzoate (871) give approximately the... 

Somewhat similar work (solvolysis of chrysanthemyl 3,5-dinitrobenzoate) has been reported by Sasaki and Ohno. 

In the solvolysis of 590 both the solvent and the dinitrobenzoate anion attack the intermediately formed cation stereospecifically (from a sterically hindered side) at the carbon separated by 4 ( ) bonds from the site of the primary ionization (>4 A). These data corroborate the intermediate formation of o,ic-delocalized ion 593 rather than the classical ion 594. 

Solvolysis of bicyclo[3,l,l]hept-6-yl, bicyclo[3,2,0]hept-6-yl, and bicyclo[4,l,0]-hept-2-yl dinitrobenzoates with a-methyl substituents gave product mixtures containing 20-35 % of 3-methylcyclohept-3-en-ol with a-phenyl substituents, no cyclo-heptene product was obtained. 

Solvolyses of trans-cyclo-oct-2-enyl-3,5-dinitrobenzoates have been studied and compared with the solvolysis of the cis-isomer. Deuterium labelling shows that little scrambling occurs, the solvent preferentially attacking the carbon originally bonded to the leaving group. ... 

Solvolysis of cycloheptatrienylcarbinyl dinitrobenzoate to give unrearranged alcohol and sytrene is believed to involve cyclopropyl participation in the norcaradiene tautomer. Paquette has studied solvolysis of several bridged cycloheptatrienylcarbinyl dinitrobenzoate and related compounds to obtain more evidence for, and information about, this cyclopropyl participation. The data obtained support the suggetion that cyclopropyl participation does facilitate these solvolyse which are proposed to occur via the equatorial conformation (256). ... 

Solvolysis rates of tertiary systems where a methyl group is present, have been used to estimate the rate of solvolysis of the corresponding secondary compounds good agreement was obtained between predicted and observed solvolysis rates for several systems which involved nucleophilic solvent assistance. Solvolysis in 60% aqueous acetone of the 3,5-dinitrobenzoate esters of cycloalk-2-en-l-ols labelled with deuterium at the 1-position, showed that little scrambling of the label or racemization occurred in the cyclo-octenol case, ca. 33 % scrambling occurred in the cycloheptenol case, and 56% scrambling occurred in the cyclohexenol case. Therefore, allylic participation, especially in the cyclo-octenol case, was rather weak. ... 

Solvolysis of the p-nitrobenzoate of (196) is ten times faster than that of (197) at 100 °C in aqueous acetone. Both give the same wide range of products, suggesting that a common ion is involved, but this intermediate must differ from the one involved in acetolysis of (198), which gives different products. Solvolyses of exo- and eni/o-dinitrobenzoates (199) (R = H, Me, Ph, or p-anisyl) have been compared. Although methyl substitution increased the rate of the less reactive exo-ester by 5 x 10 but of the endo-isomers by only 20, it has little effect on the type of product formed. The aryl substituents, unlike H and Me, led to considerable amounts of products with unrearranged skeletons. It is concluded that cyclobutyl cations will only be stable... 

Another compound for which there is evidence that hyperconjugative stabilization may be an important factor in its solvolysis reaction is 8-vinyl- xo-8-bicyclo[3.2.1]octyl 3,5-dinitrobenzoate (41), which reacts 515 times faster than its endo isomer (42) in aqueous acetone. This ratio is... 

There is very good evidence that if the cyclopropyl group of a cyclo-propylcarbinyl derivative can interact with the developing cationic center in a bisected conformation a very large rate enhancement results, whereas if this conformation is prevented sterically, there is no rate enhancement. Thus on the basis of the rate of solvolysis of 8,9-dehydro-2-adamantyl 3,5-dinitrobenzoate in aqueous acetone it was estimated that the corresponding toluene-p-sulfonate (43) would undergo acetolysis about 8 powers of 10 faster than 2-adamantyl toluene-p-sulfonate (44). It was also esti-... 

---