3base
(Hive Bee)
12-06-02 18:52
No 386903
      safrole from 4-allylcatechol + CH2Cl2 in DMF
(Rated as: excellent)
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Patent IT1299067 (italian), 2000-02-07
"new process for the preparation of 5-alkylbenzo[1,3]dioxoles from 4-vinylcyclohexenes"
antonio tozzi (endura s.p.a., italy)

equivalent: ITMI980772

Abstract:

A new 5-step process for prepg. 5-alkylbenzo[1,3]dioxoles I is disclosed [wherein: R1 = H, C1-3 alkyl; R2 = C1-12 alkyl; R3 = H, C1-12 alkyl; R4 = H, C1-8 alkyl]. The 5 steps are:

(1) metathesis or dismutation reaction of a 4-vinylcyclohexene II [Q = :CH2 or :C(cyclohex-3-en-1-yl)(R1)] with a sym. alkene R2R3C:CR3R2 [(E), (Z), or mixt.] in the presence of a metathesis catalyst, to give a 4-alkenylcyclohexene III;
(2) mono-epoxidn. of III to give an epoxide IV;
(3) hydrolysis of the epoxide IV in the optional presence of an acidic or basic catalyst to give a dihydroxycyclohexane deriv. V;
(4) dehydrogenation and/or dehydroisomerization (aromatization) of V using an appropriate dehydrogenation catalyst to
give a pyrocatechin deriv. VI; and
(5) alkylenation of VI with an alkylenating agent Z-CHR4-Y [Y, Z = (independently) leaving groups], optionally in the presence of a base as a proton acceptor, and/or in the presence of an appropriate catalyst, to give the desired product I.

The method provides a synthetic alternative to natural sources such as safrole.

For instance, 4-vinylcyclohexene was metathesized with (trans/cis)-2-butene in the presence of WOCl4 and SnBu4 at 50 in an autoclave to give 71.2% 4-(1-propenyl)cyclohexene. Epoxidn. of the latter with phosphotungstic acid and 35% aq. H2O2 in dichloroethane soln. in the presence of cetylpyridinium chloride at 70 gave 89.3% 4-(1-propenyl)-1,2-epoxycyclohexane. Hydrolysis of the latter in aq. acetone in the presence of a small amt. (0.012 equiv) of 70% HClO4 (caution: follow appropriate protocol and workup for perchloric acid) gave 90.4% 1,2-dihydroxy-4-(1-propenyl)cyclohexane. Dehydrogenation/aromatization of this compd. by autoclaving at 200 and 40 bar in the presence of ethylene and 3% Pd/C (pre-treated with H2) gave 80% 1,2-dihydroxy-4-propylbenzene. Finally, alkylenation of this diol with CH2Cl2, in a refluxing azeotropic mixt. with DMF, in the presence of KI catalyst and K2CO3, gave 5-propylbenzo[1,3]dioxole in 98% yield.

[chemical abstracts 2002 137: 154920]