Isothiocyanates isonitriles

Sesquiterpenes, sesterterpenes, dlbromotyrosine derivatives, isonitriles, isothiocyanates, polyalkylated indoles, macrolides, quinones, ancepsenolides, sterols... 

The Bu3SnH decyanation of isonitriles (Scheme 16) was first reported by Saegusa, and was developed as a general, mild method for reductive deamination by Barton and coworkers who initially showed that a variety of isonitriles, isothiocyanates and isoselenocyanates reacted with Bu3SnH under the usual free radical conditions (reflux in benzene, toluene or xylene with catalytic AIBN) to give good yields of the corresponding hydrocarbon. In concert with the normal order of radical stability, primary... 

A review on the acid promoted decomposition of a-diazoketones contains some steroidal examples.88 The full account was reported of the conversion of a-azido-ketones into cyano-carboxylic acids promoted by bromine in acetic acid.89 A general review on new reagents in natural product chemistry included the deamination of amines via the isonitriles, isothiocyanates, and isoselenocyanates reported... 

Sponges of the genus Axynyssa have been reported to produce a wide variety of sesquiterpene metabolites containing isonitriles, isothiocyanate and thiocyanates groups. Most of the interest in these compounds has concerned the biosynthetic origin of the carbon of the thiocyanate group. 

Niphatidae 140-150 160-180 Amphimedon, Cribochalina, Niphates Acetylenic derivatives, macro-heterocycles, cyclopropanic fatty acids, S/ P sterols, isonitriles, isothiocyanates, pyridine derivatives (3-alkyl pyridinium), merosesquiterpenes... 

Note that carbon monoxide inserts into the Zr-H bond of 1 (2 equiv.) to afford an T -formaldehydo-type complex [(Cp2ZrCl)]2(g-CH20) [200-202]. Iminoacyl zir-conocene complexes are formed after addition of 1 to isonitriles [203]. Carbon dioxide [183, 202] is reduced to formaldehyde with 1 (2 equiv.). C02-like molecules such as isocyanates RNCO [204], isothiocyanates RNCS [205], and carbodiimides RNCNR [204] are readily converted to the corresponding bidentate form-amido ligands. 

The first marine isocyano metabolite was appropriately named axisonitrile-1 (1) based on the trivial name isonitrile and the genus of the sponge, Axinella cannabina, which also furnished axisothiocyanate-1 (2) [1] and, subsequently, a minor constituent, axamide-1 (3) [5]. This observation that isonitriles are often accompanied by isothiocyanates (-N=C=S) and formamides (-NHCHO) was later duplicated by the Hawaiian researchers working with a Halichondria sp. In... 

In those cases where quantities of the test organisms are limited or non-aqueous conditions are preferred, blending of the lyophilized sponge with organic solvents is employed. The latter option is prudent, if one suspects the presence of reactive isocyano and isothiocyano functions. Although these isolation methods may not be unduly harsh, artifacts derived from isonitriles and isothiocyanates may arise. 

A minor isonitrile named acanthellin-2 with a specific rotation of — 24.1° was reported with no further details except some IR and MS data [3]. Isothiocyanate 15 and formamide 16 were also isolated from Axinella cannabina in a later study, in which isonitrile 14 and isomers 17-19 were also secured [35]. That 17-19 are C4(14)-ene isomers of 14 was concluded after extensive double resonance H NMR experiments. Coupling constants and nOe effects between the affected protons and various substituents of 17 established the relative stereochemistry of this series. 

Along with epi-eudesmanes, 25-27, alloaromadendranes 58-60 were separated from the chloroform solubles of a methanol extract of A. cannabina [36], As was the case with axisonitrile-2 (53), extensive spectroscopic analyses including Eu(fod)3 shift reagent experiments in XH- and 13C NMR permitted assignment of relative stereochemistry. Acanthella pulcherrima was also a source of isothiocyanate 59, although both isonitrile and formamido compounds appear to be absent [20],... 

Epipolasin-B (61), mp 92 °C, was one of two isothiocyanates obtained from the sponge Epipolasis kushimotogensis. Neither the isonitrile nor formamido analog were found with the isothiocyanate. Instead, the thiourea adduct of /J-phenylethylamine was isolated along with another isothiocyanate-thiourea pair [51]. The absolute configuration of 61 was determined by appropriate... 

Several examples of the monocyclic isothiocyano sesquiterpenoids having the bisabolane (83) skeleton are known. Along with the hydrocarbon theonellin (84), isothiocyanate 86 and formamide 87 were obtained from the Okinawan sponge Theonella cf. swinhoei. It seems remarkable, but not unusual, that not only was the amide the major constituent, but the isonitrile 85 was the missing member of the triad [57], Relative stereostructures were indicated by NMR analysis of theonellin formamide (87) and its transformation products. 

In several related studies that involved Ciocalypta and Phyllidia spp., optically inactive isonitrile 85 was part of the mixture from a Sri Lankan Phyllidia sp. The mixture also contained a minor isothiocyanate which was not identified [55]. The observation that 7-isocyano-7,8-dihydrobisabolene 88 and isocyanato 89 were obtained from separate collections of Ciocalypta spp. was surprising... 

The conversion of isothiocyanates to isonitriles under microwave conditions has been studied by Ley and Taylor using a polymer-supported [l,3,2]oxaphospholidine [119]. The use of 3-methyl-2-phenyl-[l,3,2]oxaphospholidine in solution is less favored [120] due to the associated toxicity and instability of the phosphorus-derived reagent, as well as the need to isolate the products from a complex reaction mixture by vacuum distillation. This drawback has been resolved by attaching the active [l,3,2]oxaphospholidine to a polymer matrix. 

Scheme 7.99 Conversion of isothiocyanates to isonitriles utilizing a polymer-supported [1,3,2]oxazaphospholidine.

Koenig GM, Wright AD, Angerhofer CK. (1996) Novel potent antimalarial diterpene isocyanates, isothiocyanates, and isonitrile from tropical marine sponge Cymbastela hooperi. J Org Chem 61 3259-3267. 

Cymbastela hooperi from the Great Barrier Reef contained four diterpene isothiocyanates (292-295) amongst other diterpenes [285]. An amphilectene isonitrile (296) was isolated from a Caribbean Cribochalina sp. [286]. 

The main difference in the thermolysis of tetrazolinones (44) and tetrazolinethiones (45) is the generation of sulfur (S2) and hydrogen sulfide from the latter compounds. The sulfur atom is split off from the starting molecules and not from a thermolysis product such as an isothiocyanate in a secondary reaction. The sulfurless tetrazole is then cleaved by cycloreversion, affording the corresponding isonitrile as a product that cannot be explained otherwise. There is little in common between photolysis and thermolysis of... 

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