Acid induced cationic rearrangements of carbocyclic compounds (1988)
AuthorsBright, Stevenshow all
This thesis examines fluorosulfonic acid as a reagent for use in organic synthesis. The acid strength of fluorosulfonic acid gives access to rearrangement products not available with weaker acids. The reaction of a selected series of benzyl carbinols with HSO₃F are reported. Reaction of 1-benzyl-2-methylcyclohexanol (1) gave cis-4a-methyl-1,2,3,4,4a,9a-hexahydrofluorene (2), while 1-benzyl -3-methylcyclohexanol (10) and 1-benzyl-4-methylcyclohexanol (11) were reduced to cis-1-benzyl-3-methylcyclohexane (12) and trans-1-benzyl-4-methylcyclohexane (13) respectively. [Diagram in thesis] 6-Benzylspiro[4.5]decan-6-ol (4) underwent a ring expansion to give the propellane, tetracyclo[22.214.171.124¹⁹.0²⁷]heptadeca-2,4,6-triene (5). Reaction of 1-benzyl-trans-decalin-1-ol (6) with HSO₃F gave the natural product (±)-9a-carba-14α-morphinan (7), while spiro[3-exobenzylbicyclo[2,2,1]heptan-3-endo-ol-2,1'-cyclopentane] (41) gave pentacyclo [126.96.36.199¹,¹⁴.0³,⁸.0⁹,¹⁴]octadeca-3,5,7-triene (42). The mechanism of rearrangement of 2-exo-benzylbicyclo[2.2.1] heptan-2-endo-ol (14) to 6-phenylbicyclo[3.2.1]oct-6-ene (16) was elucidated by the use of deuterium labeled substrates. Reaction of phenylethyl carbinols with HSO₃F afforded a route to bicyclic systems, for example 1-(2-phenylethyl)cyclohexanol (59) gave cis-1,2,3,4,4a,9,10,10a-octahydrophenanthrene (61) and spiro[cyclohexane-1,1-indane] (60), while 2-methyl-1-(2- phenylethyl)cyclohexanol (64) gave a mixture of cis- (65) and trans-4a-methyl-1,2,3,4,4a,9,10,10a-octahydrophenanthrene (66). [Diagram in thesis] Reaction of 1-(2-phenylethyl)-2,2,6-trimethylcyclohexanol (70) gave predominantly 1β,4aβ, 10 aβ-trimethyl-1,2,3,4,4a,9,10,10a octahydrophenanthrene (72) with a small amount of the 1a,4aβ,10aβ-trimethyl-isomer (73) while reaction of 2-exo-(2- phenylethyl)bicyclo[2,2,1 ]heptan-2-endo-ol (74) gave tetracyclo[10.2.1.0¹,¹⁰.0⁴,⁹]pentadeca-4,6,8-triene (75). Phenylpropyl carbinols provide an entry to spiro products. Reaction of 1-(3-phenylpropyl)cyclohexanol (85) gave spiro[cyclohexane-1,1-tetralin] (86), while 2-methyl-1-(3- phenylpropyl)cyclohexanol (87) gave trans-2'-methylspiro[ cyclohexane-1,1-tetralin] (88). [Diagram in thesis] 1,4-Diphenylbutan-1-ol (95) afforded 1-phenyl-1,2,3,4- tetrahydronapthalene (96) and 2,5-diphenylpentan-2-ol (97) gave an analogous product (98). 1,4-Di-(1-hydroxy-4-phenylbutan-1-yl)benzene (99) gave the two diastereoisomers of 1,4-di-(1,2,3,4-tetrahydronapth-1-yl)benzene (100), which on oxidation gave 1,4-di-(1-naphthyl) benzene (101). Fluorosulfonic acid has been shown to be a synthetic reagent for the generation of several novel spiro, reduction, cyclisation and rearrangement products not accessible under weaker acid conditions.