This review deals with higher plants that are parasitic on the roots of other higher plants. These unique organisms in the genera Striga and Orbanche, are both weeds and parasites. As weeds they show great phenotypic plas­ ticity, wide environmental tolerance, prefer permanently disturbed habitats, and are part of a plant guild associated with colonizing or crop complex species. As parasites, they depend upon another vascular plant for food or water, which flows from host to parasites through haustoria. These struc­ tures form a morphological and physiological graft with the roots or other underground parts of the host. The remainder of the root system of these parasites is usually condensed and lacks typical root hairs and root caps. All species of Orobanche and most Striga are obligate parasites-they will not develop at all without a host. Facultative parasites such as most of the parasitic species in the Scrophulariaceae are not nutritionally dependent on a host plant but they are invariably attached to one in nature. Root parasitism is found in the following diverse dicotyledon families of seed plants: Hydnoraceae, Balanophoraceae, Krameriaceae, Lennoaceae, Santalaceae (and segregate and allied families), Scrophulariaceae, and Oro­ banchaceae (88, 176). No parasitic monocots are known and there is only one parasitic gymnosperm, Parasitaxus ustus; this organism is endemic to New Caledonia-it has an unique host-parasite interface involving a graft­ like union of tissue (L. J. Musselman, unpublished).

The Biology of Striga, Orobanche, and other Root-Parasitic Weeds

Many natural products, such as the plant insecticides rotenone and ageratochromene (precocene), some fungitoxic phytoalexins, hashish constituents, vitamin E, and plant pigments, contain the chroman ring system as common structural unit. Some years ago we discovered a particularly simple entry to this class of heterocyclic compounds: The condensation of o-hydroxyacetophenones with aliphatic aldehydes and ketones in the presence of pyrrolidine leads to 4-chromanones in good yields. The scope of application and limitations as well as modification of this versatile synthesis are outlined; the accompanying tables give a good indication of the wealth and variety of possible substituents. The reaction of o-hydroxyacetophenone, e. g. with glyoxylic acid or with α,β-unsaturated ketones, proceeds atypically. The majority of the new chromanones can be used, inter alia, for the preparation of chromones, chromones and chromons, and for the synthesis of tricyclic and larger ring systems.

Synthesis and Reactions of 4-Chromanones

The purpose of this chapter is to acquaint the reader with the chemical structures of various plant growth regulators and reports of their detection from plant sources. In general only plant growth substances from higher plants are considered. Growth substances from algae have been recently reviewed by Augier (see Augier, 1978). Kochert (1978) has reviewed sexual pheromones in algae and fungi. This topic will be dealt with in detail also in a forthcoming volume of this Encyclopedia on Interactions Between Plant Cells. Secondary metabolites from bacteria and fungi that affect the growth of higher plants have been reviewed by Strobel (1974, 1977), Patil (1974), Rudolph (1976), Harborne (1977) and Tamura (1979). Letham (1978 b) has reviewed growth substances (other than the principal hormones) from both higher and lower plants.

Plant Hormones and Other Growth Substances — Their Background, Structures and Occurrence

Oxidation of 1,2-Thiazoles; A Convenient Approach to 1,2-Thiazol-3(2H)-one 1,1-Dioxides



The 1,2-thiazoles obtained from 3-chloroalk-2-enals and ammonium thiocyanate (7 9, Scheme 1) are easily transformed to 1,2-thiazol-3(2H)-one 1,1-dioxidcs 10 on treatment with H2O2 in AcOH at 80°. Hydrogenation of 10 in AcOH yields the corresponding saturated 1,2-thiazolidin-3-one 1,1-dioxides 16 (Scheme 3). Cycloalka[c]-1,2-thiazoles 18 are prepared from 2-[(thiocyanato)methyliden]cycloalkan-1-ones and ammonia (Scheme 4). Surprisingly, oxidation of 18a with H2O2 in AcOH yields the tricyclic oxaziridine 19.

Zur Oxidation von 1,2-Thiazolen : Ein einfacher Zugang zu 1,2-Thiazol-3(2H)-on-1,1-dioxiden

Isothiazole 1,1-dioxides – From Sweeter to Chiral Auxiliar in the Stereoselective Synthesis



This review gives a report of the last ten years on the new synthetic methods, reactions and biological applications of isothiazole 1,1-dioxide derivatives. the formation of monocyclic and heterocyclic annelated isothiazole 1,1-dioxides by oxidation of isothiazoles, cyclocondensation of sulfonamides and cycloaddition of isothiazol-3(2H)-one 1,1-dioxides are discussed in more detail. Furthermore, the preparation of pharmacologically important N-substituted saccharines is reported. New saccharine-derived chiral N-enoyl-and N-acyl-2,3-dihydro-1,2-benzisothiazole 1,1-dioxides serve as advantageous stereoface-directing dienophile and dipolarophile auxiliaries in Diels-Alder-reactions and 1,3-dipolar cycloadditions. Asymmetric alkylations, acylations and aldolizations are also described.

Isothiazol‐1,1‐dioxide – vom Süßstoff zum chiralen Auxiliar in der stereoselektiven Synthese

The furobenzopyran derivatives (1a) and (1b) have been prepared by a simple route from m-methoxy-phenol.

Synthesis of some benzopyran derivatives related to the seed germination stimulant of Orobanche crenata. I. 3,3a,4,9b-Tetrahydro-2H-furo[3,2-c][l]benzopyrans

The pyranobenzopyran derivatives (1a) and (1b) have been prepared by a simple route from m-methoxyphenol.

Synthesis of Some Benzopyran Derivatives Related to the Seed Germination Stimulant of Orobanche crenata Forsk. II. 3,4,4a,10b-Tetrahydro-2H,5H-pyrano[3,2-C][1]benzopyrans

Synthesis of some benzopyran derivatives related to the seed germination stimulant of orobanche crenata forsk. ii. 3,4,4a,10b-tetrahydro-2h,5h-pyrano(3,2-c)(1)benzopyrans

Die durch Kondensation von m-Methoxyphenol mit Bernsteinsaureanhydrid/AlCl3 in Nitrobenzol bzw. mit 4-Chlor-buttersaure in Gegenwart von BF3- atherat erhaltlichen Ketone (Ia) bzw. (Ib) werden unter C-Insertion (aus DMF) zu den Benzopyranonen (II) cyclisiert.

Synthesis of some benzopyran derivatives related to the seed germination stimulant of orobanche crenata. i. 3,3a,4,9b-tetrahydro-2h-furo(3,2-c)(1)benzopyrans

M. Pettett

Papers

Synthesis of some benzopyran derivatives related to the seed germination stimulant of Orobanche crenata. I. 3,3a,4,9b-Tetrahydro-2H-furo[3,2-c][l]benzopyrans

Synthesis of Some Benzopyran Derivatives Related to the Seed Germination Stimulant of Orobanche crenata Forsk. II. 3,4,4a,10b-Tetrahydro-2H,5H-pyrano[3,2-C][1]benzopyrans

Synthesis of some benzopyran derivatives related to the seed germination stimulant of orobanche crenata forsk. ii. 3,4,4a,10b-tetrahydro-2h,5h-pyrano(3,2-c)(1)benzopyrans

Synthesis of some benzopyran derivatives related to the seed germination stimulant of orobanche crenata. i. 3,3a,4,9b-tetrahydro-2h-furo(3,2-c)(1)benzopyrans