Of acylnitroso

Table 4.15 Diels-Alder reactions of acylnitroso compounds...

A new method of generation of acylnitroso compounds is the photochemical cleavage of... 

The outcome of this reaction can be rationalized by oxygen transfer from a transient intermediate (118 or an oxaziridine) to 1,3-DIBF [but see 89H(29)263]. Trapping of acylnitroso compounds yields similar products [81 JCS(P1)3250]. A similar ring-opening reaction has been observed when diarylalkylidencyclopropenes were reacted with 1,3-DIBF (93TL3131). Without citing [89H(29)263] C Moinet and co-workers reported a... 

In order to avoid decomposition of the cycloadduct, acetals have been subjected to the cycloaddition with a number of acylnitroso derivatives. The reaction proceeds with total regio- and stereoselectivity and the best yields in the cycloadduct 13 formation were obtained starting from carbamate-like derivatives66,67. 

A number of acylnitroso compounds derived from (/ )-mandelic acid or its analogs react in the cycloaddition with cyclic dienes with moderate to high asymmetric induction. The reaction is performed in methanol by oxidizing the A-acylhydrcixylamines 1 in the presence of the diene the diastereoselectivity increases by lowering the temperature (Table 3)99,10°. 

Table 3. Cycloaddition of Acylnitroso Compounds Derived from Chiral a-Hy-droxy Acids with 1,3-Dienes...

Intramolecular ene reactions of acylnitroso compounds have been studied extensively32 and used in the synthesis of alkaloids of the Amaryllidaceae family. In these cases the only-stereochemical control observed was in the cyclization to form r/s-fused bicyclo[4.3.0] systems 133,34... 

Compound 14 undergoes a retro-Diels-Alder reaction thermally at about 60°C to generate the acylnitroso intermediate which can be trapped by a different diene. Some adducts of acylnitroso compounds with cyclopenta-diene also tend to undergo facile retro-[4 + 2] reactions readily and can... 

A few examples have recently appeared involving intramolecular cycloadditions of acylnitroso dienophiles in alkaloid total synthesis. Keck has utilized such an intramolecular reaction as the key step in total syntheses of the necine bases heliotridine (21) and retronecine (22) (Scheme 3-XIII). In this work, the dimethylanthracene adduct 19 was used as a precursor for the acylnitroso compound. The Diels-Alder cyclization afforded a 1.3 1 mixture of epimeric adducts 20, which was converted to the individual alkaloids. 

However, [4 + 2] cycloadditions are usually more rapid than the corresponding ene reaction. Table 3-III shows some representative examples of Diels-Alder cycloadditions of acylnitroso dienophiles.38... 

Boger and co-workers have recently determined the regioselectivity of acylnitroso compound additions to some 2-substituted 1,3-cyclohex-adienes.5 In the cases of both electron-rich and electron-deficient substituted dienes the same regioisomer predominated by about 3 1 (Scheme 3-IX). It was suggested that the first case is consistent with a normal (HOMOdiene controlled) Diels-Alder process, whereas the second reaction is consistent with either a HOMOdiene or inverse electron demand (LUMOdiene controlled) cycloaddition. 

Acylnitroso compounds are best recognized for their ability to participate as dependable 2ir components of Diels-Alder reactions with dienes, and these observations have found substantial application in the total synthesis of natural products (Chapter 3).81 However, Mackay and coworkers have detailed the isolation of 5,6-dihydro-1,4,2-dioxazine 9a (10%) from the reaction of acylnitroso 7a with cyclopentadiene [Eq. (39)]. ... 

Although this product may arise from the [3,3]-sigmatropic rearrangement of the oxazine 8a, the acylnitroso 7b provided 5,6-dihydro-1,4,2-dioxazine 9b in excellent yield without the apparent intermediacy of the oxazine 8b.82 These observations suggest the potentially useful 4tt participation of acylnitroso compounds in Diels-Alder reactions. 

An efficient route for the construction of chiral bicyclo[4.3.1]decanes (215) has been developed " employing an acid-catalysed intramolecular carbonyl ene reaction see (214) —> (215). Optically active bicyclic lactones have been prepared by a highly diastereo- and enantio-selective ene reaction of cyclopentenes with ethyl glyoxylate. A one-pot allylic amidation which employs the ene reaction of acylnitroso compounds (216) with electron-rich alkenes has been reported see Scheme 52. 

Heating of 96 gave the desired nitrone cycloaddition product (98) in excellent yield. This reaction involved a rfJtro-1,3-dipolar cycloaddition, followed by the key intramolecular cycloaddition, another nice example of the use of a rfJtro-cycloaddition to generate a reactive intermediate for use in a pericyclic reaction (recall the generation of acylnitroso compounds via a retro-Diels-Alder reaction). 

The racemic, 5-diamino-4,5-dideoxy-lyxopyranose and 5-deoxy-5-amino-lyxopyranosylamine derivatives, (112) and (113), have been obtained from the regloisomeric cycloadducts of acylnitroso dieno-... 

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