safrole from 4-allylcatechol + CH2Cl2 in DMF
(Rated as: excellent)
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)
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.
[chemical abstracts 2002 137: 154920]