R = PhCH2CH2 35a (40%) + 36a (50%) R = 4-FC6H4 35b (79%) + 36b (15%) R = 4-N02C6H4 35c (--) + 36c (70%)

Scheme 2 Example of tandem aza-Wittig/electrocyclization [136,137] 2.1.3

The Intramolecular Aza-Wittig Reaction

The intramolecular version of the aza-Wittig reaction provides a direct route to heterocyclic ring (Scheme 3). The reactivity depends on substituents Y and R/ at the carbonyl group, and on Z and R" at the iminophosphorane; thus, a useful application has to consider the followings:

1. the ring size (formation of 5-7-membered rings ^ 4-membered ring),

2. the carbonyl reactivity (COR, COAr, RCOOR, RCONRCOR ยป RNCOR),

3. the substituents on P (PR"3 > P(Ar)3 > P(OR")3),

5. the ring strain: OS value < 20 kcal/mol (the difference of heat of formation between unsaturated and saturated analogs) [113,114].

The ring closure to a non-cumulated sulfoxide via an intramolecular aza-Wittig type reaction to construct S = N linkage has been reported recently by Hemming et al. [141].

Scheme 3 Principle of intramolecular aza-Wittig method 2.1.4

Quinazolinone Annelation

We had interest in utilizing 2-phosphoranylideneamino-benzoyl derivatives as building blocks, particularly in view of anthranilic acids as important biological precursors of various alkaloids such as glomerine, vascine, and microbial products like tryptanthrin and anthramycine [54].

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