Acid homoketonization with inversion of configuaration. Dramatic effect of water in control of stereochemistry

Acid‐catalyzed hydrolysis of bridged bi‐ and tricyclic compounds. XXXVIII—Kinetics and mechanisms of 1‐ and 3‐nortricyclanols

“…8% at the exo-6 position ( D = 1.60; besides 2% found at 1.84). The exo/endo ratio of 8:92 is in excellent agreement with that observed by Nickon et al 8 for the hydrolysis of 1-acetoxynortricyclane (1-OAc) in D 2 SO 4 -DOAc-D 2 O ([DOAc]:[D 2 O] = 1:1 or 2:1) and shows that the ratedetermining deuteration (protonation) occurs dominantly at C-2 or C-6 by retention in aqueous acids (Scheme 1). The formation of a thermodynamically stable oxocarbenium ion (SH ) is the probable reason for the relatively high protonation rate of 1-OH [k (1ÀOH)/ k (2ÀOH) % 1000; see Table 1).…”

“…The only product of hydrolysis (and isomerization) of 1-OH was identified by comparing its retention time with that of authentic 2-norbornanone (3). The formation of 3-d 1 from 1-OH was also observed in 0.25 M DClO 4 (D 2 O) (1.3 h at ca 321 K; ca 10t 1/2 ) by GC-MS. A 2 H NMR spectrum of the isolated (by CH 2 Cl 2 extraction) 3-d 1 was recorded in CHCl 3 -CDCl 3 (9:1) with TMS-d 1 (not enriched according to D) as the internal reference and the spectrum was compared with those obtained by Nickon et al 8 About 0.2 g of 2-OH was stirred magnetically with 50 cm 3 of 3 M HClO 4 (aq.) for 0.5 h (ca 1t 1/2 ) and 5 h (!10t 1/2 ) at ca 318 K in a tightly stoppered Erlenmeyer flask.…”

“…According to the product analyses (see Experimental), the only product of hydrolysis for 1-nortricyclanol (1-OH) is 2-norbornanone (3), which was also slowly formed from 1-OH during storage. The process (Scheme 1), called homoketonization, 4,8,19 is comparable with the keto-enol tautomerism, 20 both isomerizations being catalyzed by acids and bases. The mass spectrum of 3 formed in 0.25 M DClO 4 (D 2 O) shows that it contains one deuterium atom per molecule and the 2 H NMR spectrum indicates that ca.…”

Acid-catalyzed hydrolysis of bridged bi- and tricyclic compounds. XXXVII. Kinetics and mechanisms of 1- and 3-acetoxynortricyclanes

“…The syntheses of 3-and 1-acetoxynortricyclanes (1 and 2) have been presented previously. 6,7 The purities by gas chromatography (GC) were b99.5 and 97% (3% of 4-acetoxynortricyclane? ), respectively.…”