A highly stereoselective synthesis of (E)-1-substituted-1,3-dienes

(E)-1-substituted-1,3-dienes are obtained with high stereoselectivity by the thermal extrusion of SO₂ from 2-substituted-2,5-dihydrothiophene-1,1-dioxides generated by a retro Diels-Alder reaction. An application to the synthesis of (E)-9,11-dodecadien- 1-yl acetate, a sex pheromone of the red-bollworm moth is described.     

Novel synthesis of (Z)-difluoroacrylates via a highly stereoselective addition-elimination reaction

[STRUCTURE: SEE TEXT] On treating readily prepared benzyl 2,3,3-trifluoroacrylate with various Grignard reagents, e.g., aryl-, alkyl-, or alkenylmagnesium halide, in the presence of a catalytic amount of copper(I) salt in THF at -78 degrees C for 1 h, the corresponding alpha,beta-difluoroacrylates were obtained in 54-98% yields with high Z-selectivity.     

Palladium-catalyzed highly regio- and stereoselective synthesis of (1E)- or (1Z)-1,2-dihalo-1,4-dienes via haloallylation of alkynyl halides

A highly efficient and selective synthesis of (1E)- or (1Z)-1,2-dihalo-1,4-dienes via Pd-catalyzed coupling of haloalkynes and allylic halides is described. The (1E)-1,2-dihalo-1,4-dienes were generated in good yields with excellent stereoselectivities (1E/1Z up to >98/2), while (1Z)-1,2-dihalo-1,4-dienes were produced in excellent yields and stereoselectivities (1Z/1E up to >98/2) by simply adding stoichiometric lithium halides.     

Selenosulfonation of 1,3-dienes: One-pot synthesis of 2-(phenylsulfonyl)-1,3-dienes

A one-pot procedure for the transformation of a 1,3-diene into the corresponding 2-(phenylsulfonyl)-1,3-diene was developed. The reaction involves a 1,2-selenosulfonation-oxidation sequence.     

Gold-catalyzed cyclization of (Z)-2-en-4-yn-1-ols: highly efficient synthesis of fully substituted dihydrofurans and furans

[reaction: see text] The gold-catalyzed cyclization of (Z)-enynols offers an efficient and straightforward route to stereodefined (Z)-5-ylidene-2,5-dihydrofurans and fully substituted furans under extremely mild reaction conditions. Importantly, the results indicated that both the oxyauration and the proto-demetalation steps are highly stereoselective.     

Au-catalyzed synthesis of (1Z,3E)-2-pivaloxy-1,3-dienes from propargylic pivalates

Propargylic pivalates with electronically unbiased internal alkynes are selectively transformed into (1Z,3E)-2-pivaloxy-1,3-dienes containing various functionalities. The unusual selectivity of 1,2-acyloxy migration over the structurally preferred 3,3-rearrangement is realized. This reaction is highly stereoselective and offers rapid access to dienes for one-pot intra-/intermolecular Diels-Alder reactions either under thermal conditions or with Lewis acid catalysis.     

Palladium(II)-catalyzed S(N)2' reactions of alpha-allenic acetates. Stereoconvergent synthesis of (Z,E)-2-bromo-1,3-dienes.

The reaction of acetylated alpha-allenic alcohols with LiBr in the presence of 1.5 mol % of Pd(OAc)(2) provides easy access to substituted (Z,E)-2-bromo-1,3-dienes in good yields with excellent diastereoselectivity. Both secondary and tertiary acetates as well as terminal and nonterminal allenes were studied to investigate the scope and the limitations of the reaction. A mechanism is proposed to clarify how a diastereomeric mixture of the starting compound is transformed into a single diastereomer of the product.     

Novel pyridine catalysed reactions of dimethyl acetylenedicarboxylate (DMAD) and arylmethylidenemalononitriles: a stereoselective synthesis of highly substituted buta-1,3-dienes

A pyridine catalysed addition of dimethyl acetylenedicarboxylate to various arylmethylidenemalononitriles to afford highly substituted 1,3-butadienes with complete stereoselectivity is described.     

Copper-catalyzed highly efficient multicomponent reactions: synthesis of 2-(sulfonylimino)-4-(alkylimino)azetidine derivatives

[reaction: see text] Under very mild conditions, functionalized 2-(sulfonylimino)-4-(alkylimino)azetidine derivatives were prepared in good to excellent yields via a copper-catalyzed multicomponent reaction of readily available terminal alkynes, sulfonyl azides, and carbodiimides without the assistance of a base. The mechanism may be through a [2 + 2] cycloaddition.     

3,3,3-trichloropropyl-1-triphenylphosphorane: a reagent for the synthesis of (Z)-1,3-enynes, (Z,Z)-1-chloro-1,3-dienes, and 1,3-diynes

3,3,3-Trichloropropyl-1-triphenylphosphonium chloride is conveniently prepared from 2-chloroethanol, triphenylphosphine, and trichloroacetic acid. Deprotonation of this reagent generates 3,3,3-trichloropropyl-1-triphenylphosphorane, which reacts with aldehydes to give trichloromethylated (Z)-olefins, which are useful for the synthesis of (Z)-1,3-enynes, (Z,Z)-1-chloro-1,3-dienes, and 1,3-diynes in high yields and stereospecificities.     

(Z,Z)-2,3-bis(trimethylsilyl)-1,4-dibromo- and 2,3-bis(trimethylsilyl)-1,1,4,4-tetrabromobuta-1,3-dienes. Synthesis and Diels-Alder reactions.

The two title compounds (1,2) have been prepared and some Diels-Alder reactions investigated.     

Lewis acid catalyzed intramolecular Diels-Alder reactions of acyclic (Z)-substituted 1,3-dienes

Lewis acid catalyzed intramolecular Diels-Alder reactions of trienes (E,E,Z)-1a-d, (E,E,Z)-4a-d, and (E,Z,Z)-7a,b are described. Trienes containing enal or enone dienophiles cyclize in excellent yield under mild conditions using substoichiometric amounts of MeAlCl(2), in most cases with high levels of diastereoselectivity. The thermal IMDA reactions of 1a, 4a, and 7a require forcing conditions and proceed in low yield with reversed stereoselectivity in the cases of 1a and 4a.     

Domino reaction of 1,3-bis(trimethylsilyloxy)-1,3-dienes with oxalyl chloride: general and stereoselective synthesis of gamma-alkylidenebutenolides

The Lewis acid catalyzed cyclization of oxalyl chloride with 1,3-bis(trimethylsilyloxy)-1,3-dienes 3, derived from 1,3-dicarbonyl compounds 1, provides a new and general approach for the synthesis of gamma-alkylidenebutenolides 4, a pharmacologically and synthetically important class of substances. A variety of butenolides were efficiently prepared in good yields and with very good regio- and stereoselectivities. An up-scaling of the reaction was possible. The use of the Lewis acid trimethylsilyl-trifluoromethanesulfonate (TMSOTf) proved to be superior to other activation conditions. Sterically undemanding gamma-alkylidenebutenolides could be prepared alternatively by reaction of the corresponding 1,3-dicarbonyl dianions with N,N'-dimethoxy-N,N'-dimethylethanediamide (2d). In contrast to the dianion method, the Lewis acid catalyzed reaction also facilitated the cyclization of sterically hindered, base-labile, cyclic and functionalized substrates. From a methodology viewpoint, the dianion reaction represents the first cyclization of a bis-Weinreb amide and the first cyclization of an oxalic acid-synthon with an ambident dianion. The TMSOTf-catalyzed reactions are both the first cyclizations of 1,3bis(trimethylsilyloxy)-1,3-dienes with a C2 dielectrophile and the first cyclizations of 1,3-bis(trimethylsilyloxy)-1,3-dienes with a carboxylic acid dichloride or a related dielectrophile.     

Highly regio- and stereoselective four-component iodoamination of Se-substituted allenes. An efficient synthesis of N-(3-organoseleno-2-iodo-2(Z)-propenyl) acetamides

Z-selectivity was observed for iodohydroxylation of Se-substituted allenes with I2 and H2O, which is opposite to that of 1,2-allenyl sulfoxides. With n-hexane as the co-solvent Z-iodoamination leading to N-(3-organoseleno-2-iodo-2(Z)-propenyl)acetamide was observed. A brief rational for the stereoselectivity of this reaction is provided.     

Preparation and cycloaddition reactions of enantiopure 2-(N-acylamino)-1,3-dienes for the synthesis of octahydroquinoline derivatives

Stille, Suzuki-Miyaura, and Sonogashira cross-coupling reactions were carried out with a glutarimide-derived vinyl phosphate, bearing a chiral auxiliary on the N atom, to prepare enantiopure 2-(N-acylamino)-1,3-dienes as partners in Diels-Alder reactions. The cycloadditions were performed with various dienophiles under thermal conditions, with or without Lewis acids. With maleimides, the preferential formation of endo cycloadducts was observed, whereas with acrylamides the exo approach prevailed. Furthermore, in the latter case, 6-substitued octahydroquinolinones were obtained in accordance with the predicted regioselectivity. Since diastereopure compounds were in all cases obtained either by chromatography or by crystallization, and because of the easy access to a variety of boronic acids, to be used in the coupling step, this methodology is useful for the short synthesis of differently substituted, enantiopure octahydroquinolinones amenable to further transformation into decahydroquinolines possessing interesting biological activities.