Ein neuer Zugang zu 2,6,6‐Trimethylcyclohexa‐2,4‐dienon aus 4‐Oxoisophoron

Abstract

A New Access to 2,6,6-Trimethylcyclohexa-2,4dienone from COxoisophorone 2,6,6-Trimethylcyclohexa-2,4-dienone (l), a versatile starting material for the preparation of some carotenoids and several natural products, was efliciently (73 YO yield) prepared from oxoisophorone 3. After conversion of 3 to the alcohol 4 or the acetate 5, H 2 0 was eliminated (4-1) under acidic distillative conditions, whereas AcOH could be eliminated (5-+1) under Pd(0) catalysis.

Photochemistry of Bicyclo[2.2.2]oct-7-ene-2,5-diones and the Corresponding 5-Hydroxyimino and 5-Methylene Derivatives

“…Parent bicyclo[2.2.2]octene-2,5-dione was prepared from hydroquinone in 16% yield. , Yates and co-workers prepared dimethyl 6,6-dimethyl-5,7-dioxobicyclo[2.2.2]oct-2-ene-2,3-dicarboxylate by the treatment of 5,5-dimethyl-2-cyclohexene-1,4-dione with a large excess of isopropenyl acetate and dimethyl acetylenedicarboxylate . We have recently developed an efficient procedure for multigram scale preparation of 1a − d , which involves (a) the conversion of 4 to 5 , (b) the Diels−Alder reactions of 5 with acetylenes 6a − d to afford adducts 7a − d , and (c) the hydrolysis of 7a − d with K 2 CO 3 in EtOH or MeOH at 0 °C (Scheme ). The selection of enediones 1a − d as the precursors for 2 − 3 has much to do with the anticipated difference in the reactivity of the two keto groups, a feature quite critical for future manipulations.…”

4-Acetoxy- and 4-Triflyloxy-2,6,6-trimethyl-2,4-cyclohexadienones as Nondimerizing Alternatives to 2,6,6-Trimethyl-2,4-cyclohexadienone. Efficient Synthesis of Several Bicyclo[2.2.2]octenone Derivatives

“…Compound 5 was prepared from 7 following the procedure developed by Soukup et al 5 The Diels-Alder reactions of 5 with substituted acetylenes such as ethyl propiolate (8a), dimethyl acetylenedicarboxylate (8b), phenylacetylene (8c) and diphenylacetylene (8d) were performed by heating 5 with two equivalents of an acetylene derivative at an appropriate temperature to obtain the adducts 9a-d in excellent yields (Scheme 1). 8 The regioselectivity observed in the reactions of 5 with 7a and 7c is noteworthy.…”

“…During the search for an alternative to 4, 4-acetoxy-2,6,6-trimethyl-2,4-cyclohexadienone (5) prepared by Soukup et al,5 attracted our attention. Interestingly, although 5 is quite stable and accessible in large quantities its DielsAlder chemistry has not been studied.…”

“…3 It is pertinent to mention that despite the difficulties involved in the preparation and handling of 4, it has been used in the total synthesis of natural products on a number of occassions. 4 During the search for an alternative to 4, 4-acetoxy-2,6,6trimethyl-2,4-cyclohexadienone (5) prepared by Soukup et al,5 attracted our attention. Interestingly, although 5 is quite stable and accessible in large quantities its Diels-Alder chemistry has not been studied.…”

Tandem Payne/Meinwald versus Meinwald rearrangements on the α-hydroxy- or α-silyloxy-spiro epoxide skeleton

“…In the course of ongoing studies on the stereoselective synthesis of highly functionalized cyclohexane carbaldehydes, original ahydroxy-and a-trimethylsilyloxy-spiro epoxides 1 and 2 were stereoselectively prepared from phorenol. 18 Protection of phorenol as the tert-butyldimethylsilyl (TBS) ether was followed by stereoselective anti-epoxidation of the electro-deficient double bond with the nucleophilic system tert-BuOOH/Triton B. 19 Deprotection of 3 with TBAF allowed the hydroxy-directed reductive opening of the epoxide 20 to proceed in 90% yield using excess LiAlH 4 .…”