ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The acid-catalysed rearrangement of the cyclohex-2-en-1-ols 15, d3-15, 16, 17 and 19, the cyclohexa-2,5-dien-1-ols 20 and 21, and also the allyl alcohols 22 and 23 (Scheme 3), using 98-percent sulfuric acid/acetic anhydride 1:99 at room temperature, was investigated. From the rearrangement of 4-allyl-4-phenyl-cyclohex-2-en-1-ol (15), with reaction times greater than 2 hours a single product is obtained, 4-allyl-biphenyl (50) in 33% yield (Scheme 9). With reaction times below 2 hours the acetate 53 from 15 was isolated, and this could be converted into 50. The reaction of 2′,3′,3′-d3-15 in Ac2O/H2SO4 lead to 1′,1′,2′-d3-50 (Scheme 11). The rearrangement of 4-allyl-4-methyl-cyclohex-2-en-1-ol (16) (Scheme 14) yielded 39% of the corresponding acetate 60 and 30% of 4-allyl-toluene (6), which also resulted by a rearrangement of 60 under the reaction conditions. These rearrangements are all [3s,4s]-sigmatropic reactions, which proceed via the cyclohexenyl cation a (Scheme 12, R = C6H5, CH3). In Ac2O/H2SO4 the allyl-cyclohexadienes primarely formed subsequently undergo dehydrogenation to yield the benzene derivatives 6, 50 and d3-50.From the rearrangement of 4,4-diphenyl-cyclohex-2-en-1-ol (19) at 0° a reaction mixture is obtained which consists of the acetate 55, 2,3-diphenyl-cyclohexa-1,4-diene (57) and o-terphenyl (56) (Scheme 10). Both 55 and 57 are converted under the reaction conditions to o-terphenyl (56). No 4-(1′-methylallyl)-biphenyl is obtained from the rearrangement of 4-crotyl-4-phenyl-cyclohex-2-en-1-ol (17). In this case, apart from the corresponding acetate 64, a single product 5-(1′-acetoxyethyl)-1-phenyl-bicyclo[2.2.2]oct-2-ene (65) (Scheme 16) was obtained; under the reaction conditions the acetate 64 rearranges to 65.The rearrangement of 4-allyl-4-phenyl-cyclohexa-2,5-dien-1-ol (20) gives, as expected, not only 4-allyl-biphenyl (50) but also 2- and 3-allyl-biphenyl (51 and 52) and biphenyl (Scheme 13). 4-Benzyl-4-methyl-cyclohexa-2,5-dien-1-ol (syn- and anti-21) gave in Ac2O/H2SO4 at 10° as rearrangement products 93% of 2-benzyltoluene (97) and 7% of 4-benzyl-toluene (98) (Scheme 21). Hence [1,4]-rearrangements in cyclohexadienyl cations, seems to occur only to a limited extent.The alicyclic alcohols 22 and 23 (Scheme 18) gave, in Ac2O/H2SO4, as main product the corresponding acetates 73 and 75, as well as small amounts of olefins 74 and 76 formed by dehydration i.e. [3,4]-rearrangements occur in these systems. Also no [3,4]-rearrangements were observed in solvents reactions of either 4,4-dimethyl-hepta-1, 6-dien-3-yl tosulate (79; see Scheme 19) or its corresponding alcohol 24.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19750580517
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